Two unrelated sterile patients, a male and a female, with karyotypes characterized by the presence of two supernumerary bisatellited marker chromosomes, were studied with the aid of fluorescence in situ hybridization (FISH). Using alphoid centromeric specific probes, the markers were identified as an idic (15) (pter-q11) and a mar (14). In both cases a single accessory bisatellited marker was present in the karyotype of one of the parents. A possible correlation between the excess of constitutive heterochromatin and meiotic disturbances in the two patients is discussed.