White-tailed deer (Odocoileus virginianus) were sampled in a wilderness area of Southern Ontario in 1965, 1966, and 1967. Serological evidence of Leptospira pomona and L. grippotyphosa infection was found. Leptospirosis has not depressed the deer population. There was a positive correlation between age and reactor rate. Paper disc-absorbed whole blood has been tested comparatively with fluid serum and found to be a useful tool for field serological surveys.