RM-solvent spectra have been determined for two homologous series of solutes: 4-pyridyl alkyl ketones and 4-pyridyl alkyl alcohols. The substitution of the carbonyl group by the secondary hydroxyl group had little effect on the extraction strength of the solvents of class N and A; however, for electron donor solvents a marked increase of extraction was observed, the shift of the position of solvents in the spectra being approximately constant for aqueous systems. Scales of extraction strengths for various reference compounds have been compared.