The prospective screening of CF patients for prevalence of non-tuberculous myco bacteria was initiated in March 1994.As of 9/16/94, a total of 50 patients out of a projected enrollment of 50 have been screened. Three of the patients had an initial negative culture followed by a subsequent positive culture &, along with 6 matched controls, will be enrolled in Aim 2, which is intended to define the clinical course of CF patients with non-tuberculous mycobacteria.