The toxicity of the synthetic pyrethroid fenvalerate to bobwhite quail (Colinus virginianus) was examined. The acute oral LD50 to adult (19-wk-old) male and female birds was in excess of 4000 mg/kg. The LD50 to immature (5-wk-old) birds was 1785 mg/kg. Dietary toxicity testing with 2-wk-old chicks indicated an 8-d LC50 in excess of 15,000 ppm. Observed signs of intoxication included hyperactivity, irregular locomotion, ataxia, spastic muscle contraction, and, preceding death, sternal recumbency with muscle flaccidity. Significant weight loss (adult birds) or reduction in rate of weight gain (immature birds and chicks) was note generally at all dose levels in the acute testing, but only at the highest level in the dietary test. Brain residue levels associated with mortality increased with the dose (means of 0.10-1.26 ppm), whereas liver residues remained constant (overall mean of 0.74 ppm).