Sunflower seed extract (SFE) agar cultures (in petri dishes) of Lagenidium giganteum (California isolate) were evaluated for zoospore production and ability to infect mosquito larvae, Culex quinquefasciatus, after periods of storage up to 93 days at 15 degrees C. Rates of decrease in zoospore production and infectivity were related to soluble protein concentration in the SFE-agar media but at all concentrations (0.7-6.0 mg/ml) about 50% of the initial levels were lost after 40-50 days of storage. Water loss from the SFE-agar did not affect zoospore production or infectivity except at extremely high levels (about 98% water loss).