Attention has been centered on the validity of the original toxicity reports supporting the registration of pesticides. In Finland, the present standard of the toxicity reports on pesticides was studied. Of the 299 pesticide formulations on the Finnish market only 96 were supported by original toxicity reports. Altogether 16 US formulations and 121 reports, as well as 11 control formulations with 170 reports were selected for the study. Reports from the questionable laboratories proved to be invalid according to the OECD guide-lines more frequently (61%) than those from control laboratories (20%). The frequency of invalid reports among long-term studies was higher (38%) than among acute studies (26.4%). The percentage of valid toxicity studies for the registration of pesticides in Finland was increased from about 50% in the fifties and sixties to 93% in 1980. The lack of reports on old pesticide formulations rather than the validity of the toxicity reports creates a problem in pesticide registration in Finland.