The phytoestrogen, diadzein, was injected intramuscularly as [4-14-C]daidzein into two laying hens. The radioactive materials in the urine for the succeeding 23 (hen 1) or 14 (hen 2) days were fractionated on a DEAE-Sephadex column by a gradient of NaCl and the fractions thus separated were further analyzed by solvent partition, susceptability to enzymic cleavage and thin-layer chromatography. The sic following components were identified and quantitated: [14-C]diadzein, [14-C]equol, [14-C]diadzein monosulfate, [14-C]equol monosulfate, [14-C]diazein disulfate, and [14-C]equol disulfate. The urine from hen 2 yielded also the sulfate of an unidentified conversion product of [14-C]daidzein. Repeared tests for glucuronides of [14-C]daidzein or its conversion products gave negative results, excluding the possibility that any appreciable proportion of the radioactivity in the urine was in the form of beta-glucuronide. It is concluded that the diadzein and the equol excretion in the urine of the laying hen are present for the most part as monosulfates and disulfates.