Neurobehavioral effects of short-term, low-level exposure to diazinon were investigated among 99 pest control workers tested before and after their work shift with a computer-assisted neurobehavioral test battery. Each subject completed a brief neurological screening examination, a symptom questionnaire, and tests of concentration, eye-hand coordination, pattern recognition, visual memory, and finger tapping. The diazinon metabolite diethylthiophosphate (DETP) was measured in pre- and post-shift urine samples collected from 46 diazinon applicators applying granulated diazinon onto residential properties with lawn spreaders, and 56 non-applicators. Post-shift median DETP for applicators and non-applicators was 24 and 3 ppb, respectively. Full shift, whole body exposure to diazinon was quantitated for 19 subjects using personal air monitoring and passive badges. Median diazinon exposure for applicators and non-applicators was 2.1 and 0.03 mg, respectively. Mean duration of pesticide application was 39 days (SD = 12 days) before testing. No adverse DETP-related changes in pre- or post-shift neurobehavioral function were found with multiple linear regression models after adjusting for age, sex, education, and ethanol intake, although Symbol-Digit pairing speed was slower among the applicators as a group. The prevalence of 18 symptoms possibly related to diazinon exposure was not elevated among applicators. The study failed to demonstrate diverse behavioral effects of short-term, low-level diazinon exposure in a pest control program which emphasized personal protective equipment and direct supervision.