INTRODUCTION OVERALL OBJECTIVE OF THE STUDY Kerosene 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 (Saccharomyces 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. The third tier consisted of an in vivo cytogenetic analysis of rat bone marrow cells.