The authors propose two new generalizations governing the cross-linguistic distribution of radical pro drop. (1) Languages with radical pro drop have pronouns that are agglutinating for case, number or some other nominal feature. (2) Languages with pronouns that are either invariant in form or fusional for case cannot omit pronouns freely (although they may have agreement-based pro drop). These generalizations can be derived from three assumptions: (1) Spell-out rules for pronouns may target non-terminal categories; (2) pro drop is zero spell-out (deletion) of regular pronouns; (3) competition between spell-out rules is governed by the elsewhere principle. Japanese, Chinese and Jamaican Creole data illustrate this proposal.