Urine pregnancy tests performed at a large urban university student health center were examined for specific gravity to determine whether a low urine specific gravity, compared with a serum specimen, could alter the result of a urine pregnancy test. At the same time, a serum pregnancy test was performed on those samples with negative results and a specific gravity of less than 1.015. During the study period, 410 urine specimens were evaluated. Eighty of the women with a specific gravity under 1.015 had negative urine pregnancy tests with a concomitant serum specimen. The authors concluded that current sensitive immunoassay tests for human chorionic gonadotropin (HCG) are highly sensitive and that low specific gravity does not appear to alter this sensitivity.