A new bioassay method for relaxin was studied. The relaxed distance of symphysis pubis was measured by the X-ray photography and the animals giving 0.3mm relaxed distance or more were considered as respondent. A Guinea Pig X-ray Unit was established by using respondent percentage.
Comparing the palpation method of Abramowitz et al. with statistical analysis using probit, better results were obtained in the precision and sensitivity by the X-ray method.