The induction of aneuploidy in cultured Chinese hamster cells by propionaldehyde (PA) and chloral hydrate (CH) has been studied. Chinese hamster embryonic diploid (CHED) cells were grown as a monolayer in cover glasses. Treatments were performed with doses of 5 x 10(-4), 1 x 10(-3) and 2 x 10(-3)% of PA for 3 h and doses of 1 x 10(-3), 2 x 10(-3) and 3 x 10(-3)% of CH for 1.5 h. Treatments with 2 x 10(-3)% of acetaldehyde (AA) for the same PA and CH treatments were used as positive controls. Untreated cultures were used as negative controls. PA induced chromosomal aberrations with the three doses employed although in a lesser degree than the positive control. CH induced chromosomal damage only with the two higher doses. No correlation was found between the amount of chromosomal damage induced and the doses of PA or CH employed. Both compounds increased the frequency of aneuploid cells in relation to untreated controls but not in relation to the positive control. However, neither PA nor CH significantly increased the frequencies of polyploid cells. These results indicate that aldehydes and chlorine-replaced aldehydes are strong inducers of aneuploidy despite some differences between PA or CH and AA regarding cytotoxicity and polyploidy induction.