Women who visited hospitals requesting induced abortions were asked about their obstetric and medical histories by attending physicians prior to the operation. The information was solely based on their reports at the interview. The period of coverage was nine weeks, comprising six weeks before and three weeks after the onset of the last menstruation. Both the occurrence of acute respiratory infectious diseases, which included the common cold, upper respiratory tract infection (U.R.T.I.), influenza, and pneumonia, and the use of analgesics and antipyretics were most frequently reported. Regardless of whether they had an acute respiratory illness, the women who took analgesics and antipyretics (including antihistamine, cough remedy, and nasal decongestant) had 13.8% (8/58) gross chromosome anomalies. The women without the treatment had 6.3% (71/1136) anomalies. The difference was statistically significant (P less than 0.05). Triploid formation was particularly related to drug consumption, thus there were 5.2% (3/58) in the treated group and 0.5% (6/1136) in the untreated group (P=0.0074). In contrast, trisomy was not considered to be related to drug consumption on account of 8.6% (5/58) and 4.1% (47/1136) in the corresponding groups (0.10 less than P less than 0.20). When the occurrence of trisomy was examined in connection with two variables, i.e., the presence of drug consumption and the age of mothers, association was not evident (X2 assoc. = 0.883, d.f. = 1 by Cochran's method). Besides these results, neither maternal X-irradiation nor irregularity of the menstrual period was found to be related to the frequency of chromosome anomalies in the progeny.