The RBA for each steroid was calculated from the competition curves shown in Fig. 2 by using a four-parameter logistic function. Values in the first column (−HAP) represent assays performed in crude cytosol, whereas those in the second column (+HAP) represent RBAs obtained in cytosol previously adsorbed on hydroxylapatite. Data are presented as the mean ± S.E. of five independent curves, each one performed in triplicate. Differences of RBAs are significant (P < .001), with the exception of: −HAP, 11-OP versus PROG; +HAP, ALDO versus DOC, ALDO versus CORT, CORT versus DOC.