Abstract: Quantitative determinations of free amino acids in hemolymph and acid hydrolysates of midguts of female Anopheles dims infected with Plasmodium cynomolgi bastianellii were carried out and the results were compared with those of noninfected mosquitoes. On day 10 after infected blood meal, the contents of methionine, isoleucine, leucine, ornithine, lysine in the hemolymph of infected mosquitoes markedly decreased as compared with those in the controls. However, the quantitative analysis of the amino acids of the acid hydrolysates of the midguts from infected mosquitoes on day 9 after an infected blood meal showed that the content of their total amino acids was 70 % more than that in the controls, with special reference to aspartic acid, glutamic acid, valine, methionine, isoleucine, leucine, phenylalanine, tryptophan.