In a search for factors that might produce more hazardous conditions for workers exposed to pesticide residues on crops, a study was carried out to determine if the presence of the fungicides, maneb or zineb, on apple and peach foliage where parathion had been applied, affects the rate of decay of parathion residues and/or the formation of toxic conversion products such as paraoxon, thus producing more hazardous conditions for workers who enter treated areas. Results indicated that there was no significant effect by the fungicides on rate of parathion decay on apple foliage; however, with peach there was a slightly greater reduction, on an average weekly basis, where the fungicides were used than where parathion was applied alone. The data indicated that there was no measurable difference in decay rate of parathion through a 45-day period of study where the fungicides were used. Also, the fungicides did not seem to have an influence on the rate of degradation of paraoxon when it was formed on either apple or peach foliage. Thus, it appears that the presence of the fungicides on apple or peach foliage with parathion does not produce changes in residues sufficient to be considered a factor in producing more hazardous conditions for crop workers exposed to residues during thinning or picking activities in Pacific Northwest orchards.