The affinities of organic solvents in biological systems are described using solubility parameter techniques. Materials studied include lard, water, blood serum, sucrose, urea, keratin and lignin. The tendency for organic solvents to collect in fatty material, swell (penetrate) the skin, absorb into wood, or preferentially transfer to aqueous media, for example, can be estimated rapidly for any of the solvents for which solubility parameters are available.