The effects of peripheral sympathetic denervation induced by guanethidine administration to newborn and 10-day-old female guinea pigs on puberty, ovulation and the follicular population were analysed. Peripheral sympathetic denervation beginning at birth resulted in the loss of ovarian norepinephrine content (0.95. +/- 0.1 ng/mg wet tissue in untreated control animals vs non detectable in treated animals). Guanethidine administration to newborn or 10-day-old guinea pigs advanced puberty (age of vaginal opening: 27 +/- 1.2 days (newborn), 26 +/- 1.7 (10-day-old) vs 37 +/- 0.7 (control), P < 0.001) and ovulation. The number of corpora lutea in control and denervated animals was similar (3.5 +/- 0.2 vs 3.3 +/- 0.3). The relative weight (mg/100 g body weight) of the ovaries and adrenals in the denervated animals autopsied during the late follicular phase (24-48 h after vaginal opening) increased (ovaries: 27.8 +/- 1.3, 28.9 +/- 3.0 vs 20.9 +/- 0.8, P < 0.05; adrenals 36.4 +/- 1.4, 37.0 +/- 0.8 vs 31.6 +/- 1.5, P < 0.05), while the uterine weight diminished (179 +/- 13, 149 +/- 28 vs 292 +/- 20). When the animals were killed during the late luteal phase (9-11 days after vaginal closure), the relative weight of the ovaries of newborn guanethidine-treated animals was higher than that of the control animals (21.4 +/- 1.7 vs 16.8 +/- 1.4, P < 0.05). The mean number of follicles counted in the ovaries of denervated animals was significantly higher than in control animals (1736 +/- 230 vs 969 +/- 147, P < 0.05). The mean diameter of the follicles in the untouched control ovary in animals killed in the late follicular phase was significantly larger than from animals killed in the late luteal phase (263 +/- 3.9 microns vs 248 +/- 3.0 microns, P < 0.01). The mean diameter of the follicles measured in the ovaries of denervated animals was significantly higher than in controls (animals treated from birth 274 +/- 2.0 microns vs 255 +/- 2.4, P < 0.05; animals treated from day 10, 286 +/- 2.3 microns vs 257 +/- 2.3, P < 0.05). When the mean diameter of the follicles in the left and right ovary of the untouched control was analysed, the follicular diameter in the left ovary was significantly larger than in the right ovary (309 +/- 6.0 microns vs 214 +/- 3.9, P < 0.01); the response of the left and right ovaries to sympathetic denervation was the opposite. The results obtained in the present study suggest that ovarian innervation plays a role in the regulation of follicular growth, maturation and atresia which is not related to changes in steroid secretion by the ovary, but to other regulatory mechanisms.