tween as a substitute for diethyl ether in the formalin-ether sedimentation technique

background: tween as a substitute for diethyl ether in the formalin-ether sedimentation technique was evaluated for para­site detection. methods: fresh fecal material free of parasites with 10% formalin to prepare standardized specimen was thoroughly pooled. this specimen was divided into 5 equal portions; one was without infection, and each of the others was individually seeded with entamoeba coli , and giardia lamblia cysts, ova of ascaris lumbericoides , and hymenolepis nana. six hundred and eighty four slides including 228 stool samples for each of formalin-tween, formalin-ether and direct wet mount proce­dures were examined. results: the sensitivity of above mentioned procedures were computed 72.1%, 55% and 30 %; their negative predictive value were 69.3%, 58.3% and 47.3%; and their false negative error rate were 27.9%, 45% and 70%, respectively. there were no false-positive results among the 264 specimens previously identified as negative for the presence of intestinal para­sites. therefore, specificity for each technique was 100%. conclusion: in the range of our study, formalin-tween method proved to be equivalent to or better than formalin-ether tech­nique in concentrating parasite eggs, and cysts, as well as in maintaining characteristic morphology. tween is more stable, safer, cheaper, and less flammable than that of ether; and promises to be a useful alternative to ether.