The utility of comparative molecular field analysis (CoMFA), a three-dimensional Quantitative Structure-Activity Relationship (3-D QSAR) paradigm, as a tool to aid in the development of predictive models has been previously addressed (Depriest, S.D. et al., J. Am. Chem. Soc. 1993, in press). Although predictive correlations were obtained for angiotensin-converting and thermolysin inhibitors, certain inadequacies of the CoMFA technique were noted. Primarily, CoMFA steric and electrostatic fields alone do not fully characterize the zinc-ligand interaction. Previously, this was partially rectified by the inclusion of indicator variables into the QSAR table to designate the class of zinc-binding ligand. Recent advances in molecular modeling technology have allowed us to further address this limitation of the preceding study. Using molecular orbital fields derived from semiempirical calculations as additional descriptors in the QSAR table, predictive correlations were produced based on CoMFA and molecular orbital fields alone--indicator variables no longer being necessary. Arbitrary information concerning the alignment of molecules under study within the active-site introduces ambiguities into the CoMFA study. Crystallographic information detailing the binding mode of several thermolysin enzyme inhibitors has previously been used as a guide for the alignment of additional, noncrystallized, inhibitors. However, this process was complicated by the lack of parameters for zinc in the molecular mechanical force field. Therefore, zinc-ligand interactions were ignored during the standard minimization procedure. The use of field-fit minimization using complementary receptor fields as templates is presented as a possible solution to the problem. Predictive correlations were obtained from analyses based on this method of molecular alignment. The availability of crystallographic data for thermolysin enzyme-inhibitor complexes allowed for an alternate definition of the CoMFA region. Herein, promising results from analyses using actual receptor active-site atom probe atoms are presented.