In May 1976 the U.S. Environmental Protection Agency (EPA) issued a notice of rebuttable presumption against registration (RPAR) of pesticide products containing chlorobenzilate, based on a presumptive cancer risk, in the Federal Register (1976). On June 30, 1978, the EPA published a notice of determination to conclude the RPAR process in the Federal Register (1978) and in 1979 moved to cancel all non-citrus uses of chlorobenzilate, limiting use to citrus crops in California, Texas and Florida. At the time of the EPA decision several methods were available for monitoring CB residues on crops and soil. However, methods for human exposure assessment were relatively undeveloped. Subsequent to the EPA decision Brady et al. (1980) published a method whereby urinary levels of CB analyzed as p, p'-dichlorobenzophenone (DBP) could be determined. A study, on a small number of workers, by Levy et al. (1981) suggested that the method was suitable for monitoring citrus field workers for CB exposure.