This U.S.-Brazil Cooperative Science Program award will support the continuing collaboration of five condensed-matter theorists: two from the U.S.--Leo Falicov of the University of California at Berkeley and Mark Robbins of Johns Hopkins University--and three from Brazil--Belita Koiller of the Pontifical Catholic University in Rio de Janeiro, Helio Chacham of the Federal University of Minas Gerais, and Roberto Os rio of the Federal University of Bras lia. The research will focus on semiconductor alloys, fluid invasion of porous media, and pressure-induced electronic phase transitions. The project extends previous collaborative research in the U.S., while Koiller was on sabbatical at Johns Hopkins. NSF support will allow the reciprocation of this collaboration, by funding three trips by the U.S. side to work in Brazil. The project promotes cost- effectiveness by teaming a total of five different institutions, two in the U.S. and three in Brazil. Both the U.S. and Brazilian sides will contribute expertise in condensed-matter physics theory in application to this important research topic.