Five early growth characters were examined in six races of Arabidopsis thaliana (L.) Heynh, their reciprocal F(1) hybrids (1974) and F(1) by tester hybrids, using a seventh race as a paternal tester. Three of the five characters were also examined at two nutrient levels in reciprocal F(1) hybrids (1972) of all seven races. Analyses of F(1) and F(1) by tester hybrids revealed significant maternal effects in all characters examined in F(1) hybrids (1972) and in root length and plant weight of F(1) (1974) and F(1) by tester hybrids. Significant reciprocal effects were found for plant weight in F(1) by tester hybrids and for seed weight, percentage of germination and root length in F(1) (1974) and F(1) by tester hybrids. The presence of significant maternal and/or reciprocal components in both F(1) (1974) and F(1) by tester diallels suggests that differences in maternal cytoplasm rather than maternal genotype per se were responsible for much of the variation resulting from these non-direct genetic effects.