C/EBP transcription factors have been described to control the activity of the human IL‐4 promoter. The C/EBP binding sites within the IL‐4 promoter overlap with composite NF‐AT and AP‐1 binding motifs. We show here that similar binding sites are part of the murine IL‐4 promoter. Retroviral overexpression of C/EBPβ in murine EL‐4 thymoma cells led to a strong induction of endogenous IL‐4 and a reduction in IL‐2 and IFN‐γ expression. Similarily, in primary murine T cells C/EBPβ induction resulted in an increase in IL‐4 levels, whereas in human Jurkat T cells a decrease in IL‐2 RNA was detected. Like AP‐1, C/EBP factors belong to the large class of basic leucine zipper proteins. However, unlike AP‐1, C/EBPβ does not act in synergy with NF‐AT in the induction of the murine IL‐4 promoter. Instead, both factors compete in their binding to the P4/Pu‐bD site, one of the most important sequence elements of the IL‐4 promoter. Whereas NF‐AT factors require high levels of free Ca2+ and calcineurin activity for induction, C/EBP induction in T cells is Ca2+/calcineurin independent. These observations suggest that various induction conditions lead to the activation of transcription factors, inducing IL‐4 promoter activity at specific developmental stages of T cells.