The ets-1 gene is a human homolog of the oncogene v-ets of avian acute leukemia virus E26. The ets-1 gene is preferentially expressed in lymphoid cells. To understand the regulation of the ets-1 gene expression the regulatory sequences of this gene were identified and isolated. The promoter is found to be functioning in the lymphoid cell line Daudi and the erythromyeloid cell line K562 but not in the promyelocytic cell line HL60. Sequence analysis indicates that the ets-1 promoter does not contain the TATA or CAT box. It contains multiple transcription initiation sites in a tight cluster. The promoter contains one binding site each for AP1 and AP2. It has one definitive and five presumptive sp1-binding sites. In addition, the ets-1 promoter contains one ets-1 protein-binding site. Functional analysis has shown that c-jun enhances the activity of the ets-1 promoter, whereas the combination of c-fos and c-jun expressions has no synergistic effect. The expression of exogenous AP2 and ets-1 also enhances the activity of the ets-1 promoter. These results suggest that the AP1, AP2 and ets-1 proteins have a positive regulatory effect. The presence of the ets-1 protein-binding site indicates the existence of an autoregulatory mechanism for the expression of the ets-1 gene. Our results suggested that the presence of a negative regulatory element upstream of the region where most of the positive regulators are located.