The concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL), progesterone (P), estradiol (E2), testosterone (T) and cortisol have been measured by radioimmunoassay technique in daily serum samples of 10 Thai women throughout 10 menstrual cycles. The results show that in 10 subjects studied, 9 subjects show the patterns and levels of LH, FSH, E2 and progesterone suggestive of having ovulatory cycles. One subject shows no patterns of these hormones indicative of having ovulatory cycle. Daily serum PRL, T and cortisol concentrations, when determined for each individual subject for the entire cycle, varied among the 9 subjects studied. During the menstrual cycle, changes of hormones were observed in the women studied. There was a significant rise in the concentrations of serum PRL (2 subjects), T (2 subjects) and cortisol (3 subjects) on the day of the LH surge. When the mean levels of PRL, T and cortisol were plotted for 9 subjects in relation to the LH peak, there was no highly significant rise in the concentration of serum PRL, T and cortisol at midcycle.