Although sex differences in reading and related language functions have frequently been reported for both average and retarded readers, the explanations thus far proposed (maturation rate, sex-role development, textbook content, "female bias," and psycho-social factors) do not satisfactorily account for these differences. One hypothesis that might explain why girls excel boys on a variety of reading tasks is that a sex-linked inherited trait, which could be labeled "ability to acquire and process language fluently," exists. Such a trait would be formed by a complex combination of genes, since language functions depend on a complex set of sensorimotor and cognitive characteristics. A physical analogy to the trait would be height, which is polygenic and distributed differently between sexes. If this biological explanation were to hold true, it would redirect language research and instruction toward genetic considerations, promote the use of genetic counseling for early remedial intervention, and provide valuable clues toward understanding the nature of dyslexia and related language disorders. (RL)