Human endothelial cells were treated by beta-interferon with or without hyperthermia at 42 degrees C for 90 min in vitro to investigate whether these modalities were able to increase the expression of either CD54 or CD58 on the surface of the endothelial cells. The results were that the population of the endothelial cells expressing both CD54 and CD58 increased 4 days after the treatment with beta-interferon, which was independent of hyperthermia. In contrast, the primarily isolated peripheral lymphocytes from a patient with malignant melanoma (disease free state) or normal individuals responded to neither beta-interferon nor hyperthermia in terms of the expression of CD54 or CD58. These results indicate that beta-interferon may activate endothelial cells to lead to the successive activation of the other immune cells in vivo.