The relationship between plasma CORT concentration and reproductive state was investigated in New Zealand's common gecko, Hoplodactylus maculatus. This primarily nocturnal gecko has an unusual biennial reproductive cycle in which females are pregnant for about 14 months. In contrast to a previous report for a viviparous lizard, plasma CORT concentrations did not vary significantly in daytime samples among females at four different stages of reproduction (vitellogenic, mid-pregnant, late pregnant prior to winter dormancy, and spent). Significant seasonal variation in concentration (independent of reproductive state) was observed in daytime samples collected over an 8-month period (P < 0.001), perhaps reflecting seasonal patterns of growth and/or lipid deposition. Plasma CORT concentrations in summer were compared between night and day in spent and mid-pregnant females. A significant difference in concentration was detected in mid-pregnant females (P < 0.01), but unexpectedly, the concentration was higher by day than by night. No relationship of CORT with time of day was detected in spent females. There was a significant positive correlation between CORT and body temperature in day samples, but not in night samples. In contrast to many previous reports for reptiles, concentrations in females held in cloth bags showed no significant elevation during up to 2.5 hr in captivity. All groups sampled in this study had relatively low mean concentrations of CORT (< or = 6.4 ng/ml), even those held captive for up to 2.5 hr. We conclude that plasma CORT plays no obvious role in maintaining the long gestation period in H. maculatus and that relationships among CORT, activity period, and body temperature need examination in a wider range of nocturnal and diurnal reptiles before consistent patterns can be identified.