AbstractA novel description of the relationship between bioactivity and hydrophobicity, log(1/ic) = AlogP – BP+const (ic is the isoeffective concentration and P is the partition coefficient) is derived from a model for drug disposition. The function fits experimental bioactivity‐hydrophobicity profiles with a linear ascending part and a sudden drop in bioactivity after reaching the break‐point equally well as the bilinear equation and better than parabola. Due to its simplicity and fast optimization of the adjustable parameters by linear regression analysis the function is especially suitable for the use in multivariable m