Studies were conducted to determine the effect of simulated rainfall on the phytotoxicity of several herbicides. Oil soluble herbicides 4,6-dinitro-o-sec-butylphenol (DNBP), pentachlorophenol (PCP), a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4-D: 2,4,5-T), and a 2:2:1 mixture of the isooctyl esters of 2,4–13:2,4,5-T: 4-amino-3,5,6-trichloropicolinic acid (picloram) (hereinafter referred to as M-3140), usually were less affected by artificial rainfall than were water soluble 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), dimethylarsinic acid (cacodylic acid), and cis-2,3,5,5,5-pentachloro-4-ketopentenoic acid (hereinafter referred to as AP-20), on guava (Psidium guajava L.) and mango (Mangifera indica L.). Washing reduced the activity of some oil and water-soluble herbicides on sorghum (Sorghum bicolor (L.) Moench, var. Combine Kafir-60) and dioscorea (Dioscorea composita Hemsl). As herbicide rates were increased, washing reduced the phytotoxicity of paraquat and 2,4-D:2,4,5-T less on mango and guava. Artificial rainfall applied as a mist spray at different intervals had no effect on the phytotoxicity of paraquat; it reduced the activity of cacodylic acid and increased the effectiveness of AP-20 on mango.