The interaction of parameters of male and female fertility in couples with previously unexplained infertility.
 A prospective study was undertaken of the relationship between semen variables, serial endocrine and follicular ultrasound measurements in one complete menstrual cycle, and the treatment-independent chance of conception for couples who were referred with unexplained infertility.
 For the 91 couples studied, the mean length of infertility was 70 months.
 A 100% follow-up rate was achieved.
 When a stepwise analysis was performed examining semen variables and ultrasonographic and endocrine variables, the mean ratio of salivary progesterone/plasma estradiol between days +1 and +3, with respect to the luteinizing hormone surge and the Grade 2 motile sperm density, were the only variables that achieved the 5% level of significance.
 There was a highly significant relationship between the product of these two variables and the chance of conception.
 This study clearly demonstrates an interaction between parameters of male and female fertility.
