Since 1957, when Fusarium wilt was first recognized on cotton fields of the State of São Paulo, Brazil, the development of wilt-resistant cotton, adapted to field conditions of the State, has been the major goal of the breeding program at the Instituto Agronômico de Campinas. At first a large collection of cotton varieties, known as wilt-resistant, was tested in infected soil. 'Auburn 56' was selected as the most promising material. Selection for adaptation and crosses with local varieties have been made during several years. The improvement of 'Auburn 56' resulted in four varieties, IAC RM3, IAC RM4-SM5, IAC 16 and IAC 17, all of them obtained through selection in field conditions and pedegree breeding. Since 1970 only wilt- resistant varieties have been released by the Instituto Agronômico. 'Auburn 56' proved to be very suitable for adaptation to new conditions. It's resistance endured the pathogen's variation, considering the presence of race 6, and possibly of others not identified, in São Paulo, absent in the USA. The results also showed that selection for adaptation to new environments may be a powerful method of increasing variation and of breeding.