The purpose of the present study was to evaluate the pathological findings and perform morphometric analysis of the renal arteries of fetuses exposed to cocaine in utero. The control group consisted of 22 stillborn fetuses of unknown etiology whose mothers' urine was negative for cocaine or any other vasoactive substances. The study group comprised 29 stillborn fetuses whose mothers' urine was positive only for cocaine on the day of admission. Sections of fetal kidneys (4 microm), stained with hematoxylin and eosin and periodic acid-Schiff reagent, were examined under light microscopy (x40) to identify interlobular arteries. Morphometric analysis of these arteries was performed using a self-assembled system with a touch-sensitive screen as an interactive peripheral. Their inner and outer circumferences were measured by outlining them on the screen with a stylus. The radius (r) was calculated from the measurement of the circumference (2.pi.r). The difference of the radii of the outer and inner circumferences was the thickness of the arterial wall. The interlobular arterial thickness was significantly greater (P<0.001) in the cocaine-exposed group (mean 15.46+/-5.8 microm, 2SD) compared with the normal (mean 9.03+/-3.96 microm, 2SD). There was a significantly (P<0.001) positive relation with advancing gestational ages in both groups. The circumferences of the lumen of the arteries showed a significant (P<0.05) relation with advancing gestational ages in the normal group only. In the cocaine-exposed group, the arterial lumen circumference (mean 167.88+/-17.58 microm, 2SD) was significantly (P<0.001) smaller than in the normal group (mean 227.73+/-6.82 microm, 2SD). Thus, maternal cocaine abuse is associated with thickening of the interlobular arterial wall of the fetal kidney and narrowing of the lumen.