The structural basis of the induction of unscheduled DNA synthesis (UD
S) in isolated rat hepatocytes was studied with CASE, an expert system
. The analysis identified a number of structural determinants associat
ed with the induction of UDS. These structures accounted for 97.3% of
the activity of the chemicals in the database. Further analyses indica
ted that the concordance between prediction and experimentally determi
ned UDS of molecules not in the learning set is > 82%. A comparison of
predictions of UDS and mutagenicity in Salmonella indicated that ther
e is a dichotomy between these activities. The basis of this lack of c
oincidence remains to be elucidated.