SummaryIn 1961 an increase in certain congenital malformations was noticed in various parts of the Federal Republic of Germany. From the outset, it seemed very probable that a single cause was responsible, since, although these malformations varied, they appeared to belong to one and the same syndrome. For general reasons, such causes as radioactivity, contraceptives, attempted abortions or virus diseases did not provide an acceptable explanation. The epidemiology was, however, suggestive of some chemical substance taken orally.After thalidomide had been indicated in several histories, suspicion of that drug was aroused and, within one week, intake of it could be proved or was found to be very likely in 17 out of 20 cases, while in the remaining cases it could not be excluded. Though this first result was highly significant, we were at first reluctant to incriminate thalidomide definitely, because there was still some doubt about the reliability of the histories. But within a few weeks, the thalidomide aetiology received support from many sources. Specific studies on limited material are sometimes superior to extensive, broadly planned investigations.