Two unrelated patients with clinical features of 11p13 deletion syndrome, 3 years old and 3 months old, are reported. The clinical features of the patients included mental retardation, aniridia, nystagmus, blepharophimosis, and genitourinary abnormalities. Both patients were apparently free from Wilms' tumor and gonadoblastoma. Prometaphase banding analyses revealed a 46,XY,del(11)(p1300p1500) karyotype in one patient and 46,XX,dir ins(11;2)(p13;q12q23) in the other. Catalase activities in the erythrocytes in the two patients were respectively 65% and 56% of those of normal controls, close to the expected values in hemizygosity of the catalase gene. These findings confirmed a close linkage of the gene for catalase and those for the aniridia--Wilm's tumor or gonadoblastoma complex.