White-tailed deer (Odocoileus virginianus) collected in Maine (USA) from November 1988 to December 1989 were examined for Parelaphostrongylus tenuis. Relationships of deer age class, sex, collection year, and deer density to prevalence and intensity of P. tenuis infections were analyzed. Prevalence increased with deer age (P < 0.001) and interaction of deer age class and collection year (P < 0.001). Prevalence did not vary by year in deer > or = 1 yr old (85%, n = 519), but was higher in fawns in 1988 (66%, n = 87) than 1989 (23%, n = 73, P < 0.001). Based on such yearly variations, prevalence in fawns during late autumn could provide an index of annual transmission of P. tenuis. Intensity of P. tenuis averaged 2.5 worms per infected fawn (SD = 2.8, n = 72) versus 3.9 (SD = 3.1, n = 375) in deer > or = 1 yr old (P = 0.032). Neither prevalence (P > 0.50) nor intensity (P > 0.50) of infection was associated with deer density over a range of 1.4 to 5.8 deer per km2. Heads and fecal samples from the same individuals (n = 42) provided prevalence estimates of 73% and 44%, respectively. No differences in prevalence, intensity, or geographic distribution of P. tenuis in adult deer collected in Maine during fall were evident between the late 1980's (this study) and the late 1960's (Gilbert, 1973).(ABSTRACT TRUNCATED AT 250 WORDS)