In 1935 Cohen, Marrian & Watson reported that whereas nearly all of the oestrogen in the urine of pregnant women is present in conjugated forms throughout the greater part of pregnancy, labour or 'false' labour is accompanied by the excretion of considerable amounts of the 'free' unconjugated oestrogens. In the course of this work six cases of pregnancy were studied [Cohen, 1936], in two of which 'false' labour occurred about 2 weeks before the onset of true labour. In all six cases a marked rise in free oestriol excretion was observed during labour, while in the two cases referred to above, the same phenomenon was observed also at the time of the 'false' labour. The rises in the free oestrone in the urine, however, were less pronounced and were not found in every instance. The results of this work seemed reasonably conclusive, and the tentative suggestion was made that the