Using advanced gas liquid chromatography in association with multivariate statistical analysis, a study of four members of the S. damnosum complex - S. sirbanum, S. damnosum s.str., S. yahense and S. sanctipauli, revealed that both adult male and female flies could be distinguished by quantitative analysis of the cuticular hydrocarbon peaks. Adult flies were obtained from sites which were known to contain a very high proportion of pure cytospecies. The females of the complex were more readily separated from each other than were the males. On the basis of preliminary results, the technique provides for the first time, a reliable method for distinguishing S. sirbanum and S. damnosum s.str., the most important vectors of onchocerciasis in the savanna areas of West Africa, as well as an additional method for identification of adult S. sanctipauli and S. yahense. Analysis of the hydrocarbons by GC/MS showed them to be straight chain and branched saturated hydrocarbons ranging from C22-C35. The technique is simple in respect of field methods of collection, and thus holds considerable promise as a means of identifying S. damnosum complex flies throughout the area of onchocerciasis transmission in Africa.