Thirty-one penned cottontail rabbits (Sylvilagus floridanus) were used in a 2 × 2 factorial experiment to determine the effects of metazoan parasitism on selected physiological parameters of the host. The two treatments used were stomach tube administration of a broad spectrum anthelmintic and application of insecticide collars. Drug treatment caused significantly reduced numbers of nematodes, but had no noticeable effects on cestode or trematode numbers. No ectoparasites were recovered from insecticide collar-treated rabbits and only low numbers were recovered from the remaining experimental rabbits. Total serum proteins, serum globulin fractions, lymphocyte percentages, and monocyte percentages were significantly lower and neutrophil percentages were significantly higher in drug treated groups. Body weights, fat indices, selected organ weights, packed cell volumes, and basophil percentages were not significantly affected by the treatments employed.