In this paper we describe a QSAR based on biological microcalorimetry for a set of antimicrobialhydrazides acting against Saccharomyces cerivisiae and Escherichia coli. Results show thatan extrathermodynamic relationship exists based upon partitioning (log PTA) and microcalorimetrically measured biopotencies using the same cell systems. Moreover, the extrathermodynamic relationship between drug potencies for these two cell systems shows that both cellularsystems appear to behave in the same way with respect to the importance of partitioning.This means that the same set of congeneric compounds experience a similar environment inthe two systems. This represents a lateral validation of the method and discloses the validityof the QSAR model.