The genotoxic effects of 2,4,7-trinitro-9-fluorenone (129793) (TNF) were studied in a number of microorganisms. Prokaryotic cells, Salmonella-typhimurium and Escherichia-coli, and eukaryotic cells such as the yeast Saccharomyces-cerevisiae, mouse lymphoma L5178Y, and Chinese-hamster ovary cells, were used in the mutation studies. In the bacteria tests, histidine reversion and arabinose reversion forward mutation test assays were carried out; 0.1 milliliter (ml) TNF was included in the growth medium and dimethylsulfoxide (DMSO) was added to the control cells. In yeast, 100,000 cells/ml were treated with 0.1ml of TNF in yeast extract/peptone medium and controls received DMSO. Percentage of survival and aberrant colonies were scored. In Chinese-hamster ovary cells, sister chromatid exchange assay was performed using 5-bromodeoxyuridine in the absence and presence of TNF exposed in medium for 24 to 26 hours. Mouse lymphoma forward mutation assay was performed using cells and mutant frequency was evaluated. TNF produced significantly higher mutagenic responses in S-typhimurium; in contrast, TNF had no significant genotoxic effect on yeast. In E- coli, the concentration of TNF required to produce a mutagenic response was much higher compared to S-typhimurium. TNF produced complete toxicity in Chinese-hamster ovary cells at 9 micrograms/ml dose. In mouse lymphoma cells, TNF was toxic with and without metabolic activation. TNF at 1.95 micrograms/ml produced an elevated mutant frequency. The authors conclude that TNF is a potent frame shift mutagen.