Fourteen new quinoline derivatives were synthesised and their mutagenicity compared in the Ames test using Salmonella typhimurium TA100 as indicator strain with and without (Aroclor-induced) S9 mix. None of the synthesised quinoline derivatives had to our knowledge been examined before in the Ames test. Quinoline and the monohydroxyquinolines were included as reference compounds. Three of the new derivatives, i.e., quinoline 7,8-oxide, N-methyl-quinoline 5,6-oxide and trans-quinoline-5,6,7,8-dioxide appeared to be mutagenic. Quinoline 7,8-oxide was positive only in the presence of S9 mix, the specific mutagenicity amounting to 2498 +/- 96 and 1289 +/- 120 revertants per mumole with 20 and 10% S9 in the mix, respectively. Both N-methyl-quinoline 5,6-oxide and trans-quinoline-5,6,7,8-dioxide were weakly positive, the former only in the presence of the S9 mix, and the latter irrespective of the presence of S9 mix, the specific mutagenicity amounting to 134 +/- 6 and 123 +/- 10 revertants per mumole, respectively. The mutagenic potency of quinoline 7,8-oxide was of the same order as that of quinoline itself and was distinctly lower than that of 8-hydroxyquinoline. Inconclusive results were obtained with trans-7,8-dihydroxy-7,8-dihydroquinoline, 5,6-dihydroxy-7,8-epoxy-5,6,7,8-tetrahydroquinoline and 8-hydroxyquinoline-N-oxide; if these compounds are mutagenic their mutagenic potency would be at least 20-30 times lower than that of the parent compounds. None of the other chemically synthesised quinoline derivatives showed mutagenic activity with TA100 either in the presence or in the absence of S9 mix. The results obtained with the reference compounds were in accordance with literature data.