The occurrence of monoallelic expression of cytokine genes in single cells has been convincingly demonstrated, but there have been few reports of this phenomenon in T cell clones. Here we describe studies on the expression of alleles of the human genes encoding IL-2, IL-3, IL-4, and IL-13 in human CD4+ T cell clones. In contrast to the results reported in mouse T cell clones and single human T cells, we found no evidence for the monoallelic expression of the IL-2, IL-3, and IL-13 genes. The gene for IL-4 showed an imbalance in expression from each allele, indicating differential expression of IL-4 alleles within or between IL-4-expressing cells. Chemicals/CAS: interleukin 13, 148157-34-0; interleukin 2, 85898-30-2; RNA, 63231-63-0; Interleukin-13; Interleukin-2; Interleukin-3; Interleukin-4, 207137-56-2; Interleukins.