The distribution of immunohistochemically labeled HLA-DR antigen- and S-100 protein-positive dendritic cell (DR+DC and S100+DC) was investigated in 59 human esophageal squamous cell carcinomas (SCCs). A dense infiltration of both DR+DC and S100+DC was detected in 11, only DR+DC in two, and only S100+DC in one. In the remaining 45 tumors infiltrating DC were sparse. By means of double immunostaining or the mirror section method, three different types of DC, namely S-100-negative and HLA-DR-positive DC(S100-DR+DC), S-100-positive and HLA-DR-negative DC(S100+DR-DC) and double-positive DC(S100+DR+DC) were clearly identified. With regard to postoperative survival, these patients with tumors in which there was a dense infiltration of DR+DCs and/or S100+DCs showed a significantly better survival rate than those in which DC were sparse (DR+DCs - P less than 0.001; S100+DCs - P less than 0.01). These results indicate that DC infiltration may be a prognostic factor in esophageal SCCs.