To correlate ovarian growth and follicular size with 17 beta-estradiol (E2) and androstenedione (A) peripheral levels, 20 induced cycles, 6 spontaneous ovulatory cycles and 6 spontaneous anovulatory cycles from 32 women during follicular phase were examined in order to obtain a better insight in the events involved in multiple folliculogenesis. In spontaneous ovulatory cycles, a significant correlation was obtained between E2 plasma levels and volume of the dominant follicle (p less than 0.05) as well as total follicular volume (p less than 0.01). Plasma A was significantly related with sonographic features likely related to ovarian stroma as well as preantral and antral subordinated follicles, which usually fail to ovulate. Significant correlation between E2/A peripheral ratio and volume of the dominant follicle(s) was also found (p less than 0.01). In anovulatory cycles, inverse significant correlation between E2 and sonographic aspects of degenerating antral follicles (p less than 0.001) was found, whereas a positive significant correlation between E2 and ovarian stroma was obtained (p less than 0.001). No correlation between peripheral A and any ovarian sonographic compartment was evident. However in the anovulatory cycles group a significant correlation between A v E2 peripheral levels was found, too. During HMG regimen, all the ovarian compartments seemed to be responsible for E2 peripheral levels. Ovarian stroma as well as preantral and multiple antral follicles were related to A levels. E2/A peripheral ratio did not result to be a good indicator of the large follicles. During "pure" FSH therapy, exclusive correlations between estrogen and large follicles as well as total follicular volume were found.(ABSTRACT TRUNCATED AT 250 WORDS)