Spores of Nosema algerae Vavra and Undeen, N. necatrix Kramer, N. heliothidis Lutz and Splendore, and 2 unnamed Nosema species, one isolated from Malacosoma americanum (F.) and the other from Ceratomia undulosa Walker, were all germinated by a two-step procedure. The pretreatment step for N. algerae was water, and all others required a high pH in a dilute salt solution. The germination step required electrolytes at an optimal pH of about 9.5-10.0 for N. algerae, 9.0-9.4 for N. necatrix and the Nosema species from M. americanum and C. undulosa while N. heliothidis germinated best at about pH 7.0. Potassium was the most effective cation for all species, and each species differed in response to the other alkali metal ions. Between the pretreatment and germination steps, a rapid change was required or the spores would fail to germinate and require another pretreatment before germination. Based upon the results of this study, a mechanism for the germination process is proposed.