We have previously shown that androgens stimulate early stages of follicular development and that granulosal androgen receptor (AR) gene expression is positively correlated with follicular growth. The present study was aimed at elucidating potential interactions between FSH and androgens in follicular development. Study groups included eight normal cycling rhesus monkeys (five follicular and three luteal-phase), eight testosterone (T)-treated, and four FSH-treated animals. Examination of sequential ovary sections revealed selective colocalization of AR and FSH receptor (FSHR) messenger RNAs (mRNAs) in healthy, growing follicles. Moreover, individual follicles demonstrate a highly significant (P < 0.001) positive correlation between FSHR and AR mRNA levels in all study groups. Androgen treatment significantly increased granulosa cell FSHR mRNA abundance (by approximately 50-100%, depending on follicle size). FSH treatment increased granulosa AR mRNA levels only in primary follicles. The finding that T augments follicular FSHR expression suggests that androgens promote follicular growth and estrogen biosynthesis indirectly, by amplifying FSH effect, and may partially explain the enhanced responsiveness to gonadotropin stimulation noted in women with polycystic ovary syndrome.