Examined avoidance responding and plasma corticosterone levels in Long-Evans male rats (N = 50) following 0, 30, or 50 days of individual housing. Compared to the group-housed Ss, individually housed Ss showed (a) facilitated acquisition and extinction of a shuttle-box avoidance response (p < .05 and .02), and (b) significantly elevated basal level of plasma corticosterone (p < .034 and .01). These findings, together with the recent literature implicating the pituitary-adrenal axis in the control of responding in appetitively motivated tasks, suggest that the condition of housing may be a major parameter affecting performance in a variety of learning paradigms. (PsycINFO Database Record (c) 2006 APA, all rights reserved)