1. A variety of biochemical measurements were taken periodically in captive northern bobwhite (Colinus virginianus L.), European starlings (Sturnus vulgaris L.), red-winged blackbirds (Agelaius phoeniceus L.) and common grackles (Quiscalus quiscula L.) to determine whether baseline values remain sufficiently stable throughout the year for general clinical use in the absence of concurrent control specimens.

2. Variables included whole blood hemotacrit and hemoglobin, plasma lactate dehydrogenase, α-hydroxybutyrate dehydrogenase, aspartate aminotransferase, alinine aminotransferase, creatine kinase, butyrylcholinesterase, alkaline phosphatase, glucose, albumin, total protein, creatinine, urea nitrogen, uric acid, cholesterol, and triglycerides, and brain acetylcholinesterase. Butyrl- and acetylcholinesterase were included because of their specific uses in toxicology.

3. Significant seasonal differences were detected for each of the variables except brain acetylcholinesterase in at least one of the species. Significant species differences were detected during at least one season for all of the variables measured.

4. All species were maintained outdoors, but only northern bobwhites came into reproductive condition and showed sex-differences in the clinical variables during their normal breeding season.

5. It was concluded that reference values for the 18 clinical variables measured could be calculated from our data for adult specimens of the species studied, and that results for one species cannot be extrapolated with certainty to any other species.

6. Estimated normal bounds for each of the 18 variables measured by commonly used clinical procedures are presented for reproductively quiescent northern bobwhites, European starlings, red-winged blackbirds, and common grackles.