The pupal phenotypes found to occur naturally in 3 different strains of Anopheles albimanus from El Salvador were tested for their susceptibility to coindigenous strains of Plasmodium vivax and P. falciparum. The Melara strain contained both brown striped and brown stripped and brown nonstriped forms, and a significant difference was seen between these 2 phenotypes only with the mean percent infected in the P. vivax experiments. The CA109-A strain had brown and green forms which were homogeneous in their susceptibility to both P. vivax and P. falciparum. The Apastepeque strain contained brown striped as well as green and brown striped nonstriped forms. Significant differences in susceptibility to P. vivax were seen in comparisons between the base colony and each of the phenotypes as well as in comparisons between striped and nonstriped and the green phenotype. Variations in susceptibility between the base colony and the 3 phenotypes were less apparent with P. falciparum in that significant differences were seen only in comparisons between the base colony and green phenotypes. The importance of variable parasite susceptibility between and within strains of Anophelines in the epidemiology of malaria is discussed.