[en] In medical centers with many high risk pregnancies, the ability to perform a large number of urinary estriol measurements is required. The analytical procedure should provide simplicity, specificity, and economy. A solid phase radioimmunoassay is presented which utilizes antibody generated against an estriol 16-glucuronide-bovine serum albumin conjugate. The assay allows analysis of the principal component of material urinary estriol without hydrolysis or purification, with adequate specificity and the capacity for processing large numbers of samples. (U.S.)