Ran 4 strains of highly inbred mice plus complete reciprocal crosses (N = 160) under water deprivation to a criterion of at least 6 of 7 correct in 50 sessions of T-maze position reversal. Sex was of significant effect only as a basis for smaller error variance for females (p < .05). Combining abilities analysis, performed separately for males and females, indicated no significant paternal or maternal effect and no significant specific combining ability. General combining ability was a significant factor (p < .001) in the variance of both males and females and accounted, respectively, for 31.1% and 46.8% of significant genetic plus error variance. (PsycINFO Database Record (c) 2006 APA, all rights reserved)