A total of 87 brains from harvested and collected wapiti and red deer (Cervus spp.) were examined grossly and microscopically between 1973 and 1977 in a 2104 ha. preserve. Prevalence of infection significantly increased from 26.6% of the sample in 1973 to 64.3% in 1975 (P<.05). A decline to 47.7% in 1977 (P>.05) was not significant. However, the number of clinical cases was significantly higher in 1976-1977 (P<.02) than previously reported in 1973-1975.