The objective of this study was to examine the time course of changes in plasma β-endorphin and Cortisol in sheep transferred to a new environment. Three ewes and three wethers were transferred from pasture to indoor crates for a nine-week period. Blood samples were taken hourly for 24h periods once a week. β-endorphin and cortisol were measured by radioimmunoassay. Changes in hormone concentration over time were analysed by analysis of variance procedure for repeated samples. Other data were analysed by analysis of variance and Duncan's multiple range test. Mean β-endorphin concentration was significantly (P<0.001) higher in females than males at the start of the trial (1108±123 v 623±162 pg/ml). By day 60, female levels had fallen to 750±77 pg/ml but male levels were almost unchanged (561±190 pg/ml). Neither change was statistically significant. There were no significant changes in β-endorphin pulse frequency (3-4 pulses/24h) or amplitude (600-1300 pg/ml).