Folliculocentesis: a novel research technique to investigate the intrafollicular endocrine microenvironment. 
During development of the dominant follicle, the avascular granulosa cells and oocyte are exposed to the follicular fluid endocrine microenvironment.  An alteration in the endocrine characteristics of follicular fluid affects follicular steroidogenesis, oocyte maturation, ovulation and subsequent corpus luteum function.  In-vitro studies on pooled follicular fluid from ovarian specimens lacked temporal precision between menstrual and follicular endocrine events.  We have established a new technique, termed folliculocentesis (FC), to sample follicular fluid from the dominant ovarian follicle without compromising its growth or function during the mid- to late follicular phase.  A total of 38 subjects with regular ovulatory cycles each underwent two identical cycles of hormone and follicle growth monitoring: one cycle served as the control, and FC was performed during the second cycle.  During all cycles, plasma luteinizing hormone (LH), oestradiol and ultrasound monitoring of follicle growth were commenced on day 7 and continued until after ovulation.  During FC cycles, 200 microliters of follicular fluid were aspirated from the dominant follicle using transvaginal ultrasound guidance when the follicle diameter reached > or = 10 mm.  Six subjects were excluded from the study because of incomplete or invalid endocrine data.  In all, 32 subjects completed both the FC and control cycles.  The follicle growth pattern, maximum follicle diameter, plasma oestradiol, oestradiol peak, plasma LH, LH surge and follicular phase length were similar during FC and control cycles.  A total of 50 valid follicular fluid samples were obtained when the dominant follicle was sampled once, twice or three times during the same cycle and from the same follicle in 15, 16 and one subjects respectively.  The follicular fluid samples contained steroid concentrations consistent with those of the mid- to late follicular phase.  We conclude that the FC procedure is safe, easy to perform and does not affect follicle growth or hormone dynamics.  Analysis of the follicular fluid samples is expected to provide us with valuable in-vivo information about ovarian endocrinology.