Field tests using Nosema algerae Vavra and Undeen against Anopheles albimanus Wiedemann conducted in the Panama Canal Zone resulted in infection of An. albimanus in all test plots. Infection rates were dose-dependent and ranged from 16% in a test area of 1,100 m² given a single application at a rate of 2.15 × 10⁷ spores/m², to 86% in a test plot of 37 m² that received 4 treatments at a rate of 2.15 × 10⁹ spores m². Many infected larvae brought to the laboratory died before pupation, and microscopic examinations showed that these larvae were heavily infected with N. algerae. Nosema algerae, therefore, will produce infections and mortalities in natural populations of An. albimanus.