A classification of pesticides according to their carcinogenic hazard is presented. It is part of a more comprehensive classification of toxic, mutagenic and other pesticides. All the agents are divided into four classes: extremely hazardous, hazardous, moderately hazardous and slightly hazardous. Class I corresponds to Group 1 of the classification of the International Agency for Research on Cancer (IARC)-the agent confirmed as hazardous to humans. Class 2 (hazardous agents) is subdivided into three subclasses (2A, 2B and 2C) to ensure a more differentiated approach to evaluation of pesticides; the corresponding group of the classification is divided into two groups. Like group 3 of the IARC classification, class 3 (moderately hazardous agents) covers substances with limited evidence of carcinogenicity to animals. Unlike the IARC classification, it does not include unclassifiable agents which are not subject to consideration when pesticides are submitted for registration. Another distinction from the IARC group 3 is the inclusion of agents on sufficient evidence of their carcinogenicity but obtained with maximum tolerated dose only. Regulatory actions to be taken depending upon the class of hazard are discussed.