The present study is designed to elucidate certain biological characteristics of urinary chorionic gonadotropin and to see what differences could be demonstrated between HCG in normal pregnancy and in the trophoblastic diseases. We have attempted the biological characterization of HCG using crude HCG and the purified HCG (12, 000 I.U./mg) by zone electrophoresis on starch grain and chromatography on DEAE cellulose. Evidence has been presented that urinary HCG extracts are fractionated into two or more biologically active components. The one component has predominantly FSH activity and the other predominantly LH activity. Furthermore, our present investigation revealed possible differences between the gonadotropin in the urine from pregnant women and from patients with trophoblastic tumors.