XRR 185A (TACU no. 8259) was tested in the Ames Salmonella Pre-Incubation Assay with metabolic activation by Aroclor 1254 induced rat liver homogenate (S-9) at doses of 1.0 micro1, 0.50 micro1, 0.30 micro1, 0.10 microl and 0.05 microl test substance per bacterial plate and without metabolic activation by S-9 at doses of 0.10 micro1, 0.07 microl, D.05 microl, 0.03 micro1 and 0.01 micro1 test substance per bacterial plate in strains TA98, TA100, TA1535, TA1537 and TA1538. In preliminary toxicity studies at a dose of 0.30 microl/50 microl without S-9 in tester strains TA100 and TA1537 the background bacterial lawn was extremely reduced and microcolonies were present. In both of these tester strains at a dose of 3.1 microl/50 microl with S-9 the background bacterial lawn was moderately reduced. The reduction of the background bacterial lawn and the presence of microcolonies indicate sufficient solubility for interaction of the bacteria with the test material . The results of the assay indicate that XRR 185A had no mutagenic activity in this test system.