background: the serum levels of c 3 , c4, and the total hemolytic activity of complement system (ch50) of patients ex­posed to mustard gas (mg) in the battlefield were measured in this study. methods: c3 and c4 were measured by single radial immunodifusion and ch50 was evaluated according to total hemolytic activ­ity of the serum. results:   the serum levels of c 3 showed a significant increase...