Oleylamine was tested for mutagenicity in vitro in Chinese hamster ovary (CHO) cells, both in the presence and absence of Aroclor-induced rat liver S-9 metabolic activation. Based on preliminary determinations of cytotoxicity, the compound was tested in 3 trials without activation at concentrations of 0, 0.1, 0.5, 1.0, 1.5, or 2.0 nl/ml, and 0, 1.0, 1.5, or 2.0 nl/ml (repeated once), and in 3 trials with activation at 0, 5.0, 6.0, 7.0, 8.0, or 9.0, and 0, 7.0, 8.0, 9.0, 9.5, or 10.0 (repeated once). Cell survival without metabolic activation was concentration-related and ranged from 102 to 62% at concentrations from 0.1 to 2.0 nl/ml. Cell survival with metabolic activation was generally concentration-related and ranged from 137 to 5.5% at concentrations from 5.0 to 10.0 ul/ml. In the first trial, a very large increase in the frequency of mutations at the HGPRT locus was observed at 2.0 nl/ml without activation (136.4 mutants/10E4 cells), and at 9.0 nl/ml with activation 109.4 (mutants/10E4 cells); no increase in mutation rate was observed at other concentration levels in this trial. In the second and third trials, the treatment did not increase the frequency of mutations at the HGPRT locus, either with or without metabolic activation; the authors concluded that the positive results in the first trial were anomalies, and that the test compound was not mutagenic in CHO cells under the conditions of this experiment.