The urinary excretion of 4,4'-methylene-bis-ortho-chloro-aniline (101144) (MBOCA) was investigated in rats as a means for biological monitoring after skin application and gavage. Male Sprague-Dawley- rats were treated with MBOCA and carbon-14 (C-14) labeled MBOCA by gavage or by drops onto a shaved 6 centimeter square area on the back. Urine and feces were collected from the gavage treated animals at 24, 48, 72, and 96 hours after MBOCA administration. Twenty four hour urine samples were collected from some of the skin exposed animals. The skin exposed animals were sacrificed at 1, 2, 4, 8, or 24 hours post MBOCA application. Skin samples were analyzed by liquid scintillation counting after tissue digestion, and the urine samples were analyzed by gas chromatography. The rate of excretion of the labelled MBOCA was high within the first 24 hours for the gavage treated animals. Approximately 16.5 percent of the labelled compound was excreted as C-14 in the urine of the gavage treated animals after 72 hours compared to only 2.54 percent for the skin exposed animals. Approximately 0.25 percent and 0.008 percent of the MBOCA was excreted as the parent compound in the urine of the gavage treated animals and skin exposed animals, respectively, during the same period of time. The amount of MBOCA detected in the urine after skin application was reduced by washing the skin within the first 8 hours after treatment. The authors conclude that urinary analysis of MBOCA is not a precise indicator of recent exposure.