Conscious unrestrained rats were stimulated through chronically-implanted electrodes in the median eminence-arcuate (ME-ARC), medial preoptic area (MPOA), amygdala (AMYG) or caudateputamen area of the brain on diestrus-2 of a 4-day estrous cycle or diestrus-3 of a 5-day cycle. Each rat was repeatedly tested after returning to normal cycles according to the following procedure: stimulation at current levels of 25, 50 or 100 muA (biphasic pulses), injection of 1 or 3 mug estradiol benzoate or 1 mg progesterone, and injection of the same hormones 24 h before stimulation at 50 muA. Indirect evidence of advanced ovulation, judged by the pattern of vaginal smears, was obtained depending on the current and site of stimulation: 25 muA was subthreshold for all brain areas, 50 muA was threshold for the ME-ARC and AMYG, and 75-100 muA was very effective in the ME-ARC, but could not be tested in the MPOA or AMYG due to abnormal behavior. Histological studies of the ovary revealed premature luteinization of some follicles and occasional advancement of ovulation. Pseudopregnancy-length diestrus often followed ovulation or advanced ovulation. This event was produced by a lower threshold current of 25 muA in the ME-ARC and MPOA. A current of 50 muA was maximally effective in the ME-ARC, but less so in the MPOA and AMYG; 75-100 muA caused successive periods of pseudoprengancy-length diestrus in the ME-ARC group. It is concluded that specificity of neural circuits from the AMYG to LHRH neurons is questionable since stimuli which led to reproductive changes also produced seizure activity. But stimuli producing no abnormal behavior in conscious rats clearly altered reproductive cycles when applied to the ME-ARC, and in the MPOA produced mino changes in cycles. Estradiol facilitated the effect of stimulation on early appearance of leucocytes in the vaginal smear in the estrous cycle and pseudopregnancy-length diestrus; contrarily, progesterone, in a few cases, inhibited both effects.