A reliable radioimmunoassay for rat serum corticosterone has been developed. 25 μ1 of diluted serum (1:100) was assayed with a specific antiserum raised against corticosterone-21-hemisuccinate conjugated to bovine serum albumin. The within-assay and between-assay coefficients of variation were 7.1% and 13.9%, respectively. The mean serum corticosterone concentration was 65.3±6.0 ng/ml (n=10). The corticosterone level increased to 208.4 ±23.7 ng/ml after ACTH administration, and was suppressed to the limit of assay sensitivity after dexamethasone administration
