DNA from 76 cases of acute lymphoblastic leukemia (ALL) was tested with a cDNA probe encoding the alpha 2B interferon (IFN) gene transcript. Deletions were found in three of ten pre-B, three of 21 T-cell, four of 22 common and one of 23 null ALL cases. Amongst those with null ALL were 20 infants, most with characteristic translocations, none of whom had deletion of alpha IFN genes. The results confirm that alpha IFN gene deletions may occur without visible abnormalities of chromosome 9p and show that they occur across a wide range of ALL phenotypes. The results suggest that alpha IFN gene deletions may be rare events in null ALL of infants but their incidence and cellular consequences remain unknown.