The antiarrhythmic activity of propranolol analogues, the inotropic activity of propranolol analogues, the anti-inflammatory activity of anthranilic acids, the hypnotic activity of barbiturates, and the inhibition of cell division by barbiturates were correlated with either octanol--water partition coefficients or with high-pressure liquid chromatographic retention indices. The retention index, which was a scale based on the relative retention of the drug and a series of C3--C23 2-ketoalkanes, was found to give higher correlations with biological activity than was found between octanol--water partition coefficients and biological activity. Only in the case of the anthranilic acids was the retention index found to give the lower correlation.