Entomophaga grylli (Fresenius) Batko (North American pathotype 1) is a fungal pathogen of the clearwinged grasshopper, Camnula pellucida (Scudder). We present results from a field experiment conducted in Arizona in 1984, designed to investigate factors associated with seasonal patterns of cadaver persistence and sporulation by E. grylli. Rangeland plots at two sites were monitored daily for 8 weeks for the appearance of new cadavers of diseased grasshoppers during a natural epizootic. Cadavers were individually marked and revisited on subsequent days, when it was noted whether or not conidial sporulation was underway. Environmental variables were recorded by electronic data loggers. Daily probabilities of cadaver disappearance and fungal sporulation were analysed in relation to site, date, and various measures of cadaver status, sporulation history, and environmental variables by logistic regression analysis. The average daily rate of cadaver disappearance was 0.22, yielding an expected time to 50% disappearance of 2.8 days. The environmental factor most significantly associated with cadaver disappearance was rainfall, and the most important host factor was age of the cadaver. The probability that conidia would be discharged from a cadaver over the next 24 h was most dependent on whether or not conidial sporulation was underway already. This probably reflects a state of readiness for sporulation on the part of the fungus. Although the probability of sporulation declined with increasing age of a cadaver, high rates of sporulation were predicted under conditions of prolonged leaf wetness and high humidity at night, regardless of age of the cadaver. These results, together with the observation that in some cadavers sequences of sporulation were interspersed with periods of no sporulation, suggest that E. grylli may undergo cycles of dehydration and rehydration, in which conidial production is interrupted and then resumes in response to changing environmental conditions.