1,066 urine samples were assayed by β-human chorionic gonadotrophin (β-hCG) monoclonal pregnancy test with a sensitivity of 150 IU hCG/l Tests were performed in 5 independent laboratories and results were compared with those of pregnancy tests which were used routinely. Urine samples which showed discordant results under evaluation were reas-sayed for β-hCG using radioimmunoassay. 569 urine samples were from nonpregnant women, and a consistent result with comparison pregnancy tests was achieved in 97.19% of urine samples. The trial test from 389 urine samples of pregnant women was 99.49% in accordance with routine pregnancy tests. Results from 108 urine samples of women over 40 years of age indicate the high specificity of the new β-hCG monoclonal pregnancy test. Titration experiments showed 63% positive tests at 150 IU β-hCG/l Data presented combine to suggest that this new monoclonal pregnancy test is a valuable aid in diagnosing early pregnancy. It may also be used in the diagnosis of tubal pregnancy and in other ectopic processes.