This study attempts to account for the distributional restrictions of Japanese head-internal relative clauses, and the restrictions on accessibility of noun phrases to head internal relativization in terms of the Empty Category Principle (ECP). The data indicate that there is a subject/object asymmetry in the distribution of the head - internal relative clauses, suggesting an account by the ECP. Head-internal relatives also have a curious restriction on the accessibility of the noun phrase to relativization. (MSE)