Abstract: Tne acoustic nonlinearity parameter B/A is measured by using finite amplitude insert-substitution method. For lossy media the sound attenuation of samples must be acounted for in the determination of nonlinearity parameter B/A. Considering the influence of both sound attenuation and diffraction of the transducer on the experimental measurement, a modified formula for B/A values is derived in this paper. On the basis of this formula, the B/T values and its dependence on the concentration and the structure of biological samples, including biological solutions and soft tissues, have been studied.