INTRODUCTION Rubber Solvent (CHF-32-263) was evaluated for mutagenic potential and germinal cell risk in a three tier testing approach. The first tier consisted of in vitro microbial assays in which the test chemical was screened for mutagenic and recombinogenic activity using bacteria (Salmonella typhimurium ) and yeast (Saccharymces cerevisiae) in both plate and suspension techniques. The second tier consisted of screening the compound for mutation induction in cultured mammalian cells (L5178Y@ TK+/-) in vitro. Assays in the third tier were in vivo and consited of a cytogenetic analysis of bone marrow cells and a dominant lethal assay on rats treated with Rubber solvent.