Inhibin B is a product of the gonads and a marker for ovarian follicular development. This was a cross-sectional study designed to assess awakening of the reproductive function by studying secretion pattern of inhibin B during the weight restoration in patients with anorexia nervosa (AN). Twenty patients with AN participated at low weight [body mass index (BMI) 14.3 +/- 0.3 kg/m(2))], 22 partially weight recovered AN (BMI 17.4 +/- 0.1 kg/m(2)), 16 reached goal weight but did not restore menstrual cycles (BMI 19.5 +/- 0.1 kg/m(2)), and 13 reached goal weight and had at least six consecutive menstrual cycles (BMI 19.3 +/- 1.0 kg/m(2)). Nineteen eumenorrheic females with BMI 19.8 +/- 0.4 kg/m(2) served as controls. At low weight, patients had low basal leptin, inhibin B detectable in only 15% of samples, and LH significantly lower than in controls (P < 0.01). At weight gain, basal leptin increased, median inhibin B increased (detectable in 66.7% of samples), and LH remained low, all significantly lower than in controls (P < 0.01). Weight-recovered/amenorrheic patients further increased basal leptin, inhibin B was detectable in all samples, and LH remained low, all significantly lower than in controls (P < 0.01). In weight-recovered/cycling patients, basal leptin, median inhibin B, and LH, as expected, were not different from healthy volunteers. Inhibin B values correlated significantly with leptin (P = 0.000) and BMI (P = 0.000). In summary, gonads in patients with AN who gain weight are not entirely quiescent but have a low level of activity. Inhibin B is an early marker of gonadal activity, and with weight gain, awakening of the reproductive function is gradual, whereas factors triggering the onset of menstrual cycles still remain unknown (nutritional fat intake, psychological).