Rapid, sensitive radioimmunoassays have been developed for the conjugated primary bile salts, cholate and chenodeoxycholate, using immunogens prepared by the mixed anhydride procedure. Antibodies produced showed equal specificity for glycine and taurine conjugates. Cross-reactivities were comparable with those from other published radioimmunoassays. The assays were routinely performed on unextracted sera and the concentrations correlated well with concentrations determined by gas-liquid chromatography. Accuracy, determined by the addition of bile salt to charcoal-extracted serum, and percision, determined by replicate analysis of a normal sample, were both less than +/- 10%. These figures are comparable with those obtained by both gas-liquid chromatography and other radioimmunoassays for bile salts. Normal sera were found to contain 0.49-1.32 mumol/l of cholate and 0.55-2.02 mumol/l of chenodeoxycholate. Serum concentrations in patients with liver disease were higher than this normal range. Three patients with mild liver distrubance were found to have one bile salt in the upper limit of normal, but in each case the other primary bile salt was outwith the normal range.