nitric oxide (no) is a small molecule synthesized by most of mammalian cells with diverse biological activities including vasodilatation, host defense and wound healing. impaired wound healing is a common occurrence among diabetics and patients receiving glucocorticoid therapy. on the other hand the application of laser in biomedical area have been increased. thus, the current studies were designed to investigate the effect(s) of low level laser (lll) on wound healing and no production in diabetic, cortisone acetate-treated and normal control of sd wounded rats. materials and methods: in this study 60 male sd rats (150-200 gr) were used and randomly divided into 6 groups: group 1 control laser (cl), group 2 control no laser (cnl), group 3 diabetic no laser (dml), group 4 diabetic laser (dml), group 5 cortisone acetate no laser (canl) and group 6 cortisone acetate laser (cal). rats in group 3 and 4 were made diabetic by i.p. injection of 55 mg/kg stz before wounding. steroid-treated rats were given 10 mg/kg i.m. cortisone acetate. all rats were anesthetized by i.p. injection of mixture of ketamin (10%) and xylazine (2%). the dorsal side of rats were shaved, swabbed by alcohol and a full-thickness wound was made by removing panniculus cornosus after surgery wound imaging were done for each rat and two laser were applied as follows: l1:670nm on wound bed for 20 seconds l2:810nm on wound margin for 40 seconds percent open wound area (powa%) were calculated as the index of wound-healing during the course of study. urine samples (24-hour intervals) were collected for each rat before and after wounding. samples were frozen until equipment. for pathologic analysis wound samples were taken on days 12 and 22 post-wounding and measurements were reported as total scores for corresponding days. statistical analysis were performed using a paired two-tailed student’s t-test to assess significant differences in wound- healing. an unpaired two-tailed student t-test was used to assess significant differences in urinary no?? output as indirect measure of no production. other analysis were done using spss software version 11.5 and p?0.05 was used to determine significant differences. results : wound closure profiles for cl and cnl groups showed no any significant differences . there was a slight faster healing for cl group on days 12-15 post-wounding but there was no significant differences as compared to cnl group. upon wounding both groups showed an increased urinary no?? output from days 1through 15 post- wounding with no any significant differences between two groups.wound closure profiles for dml and dmnl groups showed a significant differences on days 12 through 20 post-wounding. the urinary no?? profiles also showed a significant increase and differences from days 1 to 17 post-wounding. wound closure profiles for cal and canl groups showed a slight improvement in healing for cal group on day 12 to 15 post-wounding .urinary no?? profiles for cal group showed an increase on days 1 through 14 post-wounding as compared to canl group. the total pathologic scoring for dml group for wound margin was significantly higher than dmnl group. the total pathologic scoring for both cl and cnl groups showed no any significant differences. while the total pathologic scoring for cal group either for wound context and wound margin showed a significant differences (p?0.05) . in addition, the total pathologic scoring for dml group vs dmnl group on day 22 post-wounding was significant. there were no any significant differences for cl, cnl, cal, and canl groups on day 22 respectively . discussion and conclusion: it has been reported that no production during wound healing is an index of healing. usually upon wounding no will increase dramatically for next few days post-wounding for control animals, then will decrease as wound heals, as the results of urinary no?? output of this research confirmed this concept. on the other hand, no production will be attenuated for impaired wounds, but upon wounding there would be an increase of no production to some extend that is because of activity of other cells producing no that has not been inhibited by impairment factors such as glucocorticoids . the application of low level laser on dml group in this research showed a dramatic effects on cell activation or bio-stimulation of wound closure profile for dml group. also, the application of laser had an effects on wound-healing and cocomittant increase in no production for cal group. pathologic studies and slides from this research revealed that laser application on wound impaired had its effects by improving pathologic parameters such as collagen deposition and vascularity. in conclusion the findings of the current research revealed that laser has modulatory effects on normal wound but bio-stimulation on impaired wounds probably through bio-chemical pathways. however, much need to be done for complete elucidation of the effects and mechanism of low level laser on wound-healing. key words: nitric oxide (no), wound-healing, laser, diabetic, cortisone acetate