Anionic acid phosphatase (AP) isozymes in stem homogenates of flax genotrophs L and S were examined electrophoretically. The banding pattern was similar in both genotrophs. Relative mobility (Rm) was faster in each band of L than in the corresponding band of S. These Rm shifts did not result from differences in the sample concentration or from differential rates of development. AP activity was the same in both genotrophs. The banding pattern of FI hybrids resembled the parental pattern. No multiple banding was observed in any of the F1 bands. The R m in the FI hybrids showed a dominance of L. Plots of loge (Rm) against gel concentration were constructed. While the Y intercepts of the plots indicated some differences in free electrophoretic mobility, molecular conformation was the major factor underlying both the Rm differences between bands and the R m shifts between L and S, for corresponding bands. Estimates of apparent molecular weight (MW) for the different bands ranged from 25,000 to 250,000, with a strong possibility that some bands were oligomeric forms of others. Apparent MW was, on average, 17% higher in S than L.