In a study designed to investigate genotype-environment interaction, eight strains of laboratory rats were crossbred in a replicated diallel cross employing infantile stimulation and its absence as environmental treatments. This paper reports on measures of the acquisition of two-way escape-avoidance conditioning, comprising number of avoidances, avoidance and escape latencies, and intertrial and presessional crossings, which were subjected to biometrical genetical analysis, all but the last successfully. Additive variation was prominent throughout and some measures showed directional dominance. Effects of stimulation were seen in avoidance number and crossings. The analysis of avoidances by successive blocks of trials using covariance:variance graphs revealed differences in the way the strains varied with respect to the changing relationships of proportions of dominant and recessive alleles governing this behavior. The results are discussed in the light of previous data and of their evolutionary implications.