FSH and LH concentrations during the menstrual cycle are well known, showing characteristically a midcycle surge in LH as well as in less degree in FSH. At the present there is an increasing interest in studying variations of the moleculoar forms of both gonadotropins. We have studied the chromatographic profile of FSH and LH in sera obtained from women regularly ovulating and in patients with anovulatory cycles by the use of gel column chromatography. It was observed the predominance of LH 32-34 kDa at midcycle and the heterogeneous FSH profile during the ovarian cycle. In sera from anovulatory patients the chromatographic profile was even more irregular for both LH and FSH. It is concluded that LH 32-34 kDa may be the more biological isoform in turn related with the process of ovulation.