Every null-additive set is meager-additive

It is proved that every null-additive subset of^ω2 is meager-additive. Several characterizations of the null-additive subsets of^ω2 are given, as well as a characterization of the meager additive subsets of^ω2. Under CH, an uncountable null-additive subset of^ω2 is constructed. Publ. No. 445. First version written in April 1991. Partially supported by the Basic Research Fund of the Israel Academy of Sciences and the Edmund Landau Center for Research in Mathematical Analysis, supported by the Minerva Foundation (Germany).