Ovulatory activity in Creole goats maintained under two different photoperiodic conditions. Two groups of Creole female goats were maintained in light-proof rooms and subjected to either simulated temperate photoperiodic conditions (TE solid line closed circles, 16 goats, 8 to 16 hours of light per day from winter to summer solstice), or simulated tropical photoperiodic conditions (TR dashed line open squares, 17 goats, 11 to 13 hours of light per day from winter to summer solstice) for 33 months. Ovulatory activity was assessed by twice-weekly (first 25 months), then once-weekly (last 8 months) determinations of plasma progesterone by radioimmunoassay. Results are expressed as the percentage of female goats experiencing at least one ovulation per month. Significant differences between groups are indicated.