Intercellular adhesion molecule-1 (ICAM-1) expression by tumour cells may be involved in their interaction with defensive cells. In this study the surface ICAM-1 expression and soluble ICAM-1 (sICAM-1) production by five small cell lung cancer (SCLC) and five non-SCLC (NSCLC) cell lines was investigated. In addition, the effects of ICAM-1 upregulation by cytokines on the adhesion of lung cancer cells to allogeneic lymphokine-activated killer (LAK) cells and susceptibility to LAK cytotoxicity was also evaluated. ICAM-1 expression was assessed by flow cytometry. Soluble ICAM-1 release was measured by enzyme-linked immunosorbent assay (ELISA). Interaction with LAK cells was tested by adhesion and cytotoxicity assays. At baseline, SCLC lines did not express ICAM-1, while 4 of the 5 NSCLC lines expressed ICAM-1. ICAM-1 expression was induced by interferon-gamma (IFN-gamma) in 4 of the 5 SCLC lines and upregulated in 1 of the 5 NSCLC lines. ICAM-1 expression was induced by tumour necrosis factor-alpha (TNF-alpha) in 1 of the 5 SCLC lines (National Cancer Institute (NCI) H211), and upregulated in 2 of the 5 NSCLC lines (NCI H460 and NCI H838). Among the latter lines, one (NCI H838) released significant amounts of sICAM-1. Adhesion to LAK cells and susceptibility to LAK cytotoxicity were significantly higher in TNF-alpha-treated NCI H460 and NCI H211 cells, compared to untreated NCI H460 and NCI H211 cells. In contrast, no difference in adhesion to LAK cells and susceptibility to LAK cytotoxicity was detected between baseline and TNF-alpha-treated NCI H838 cells. Intercellular adhesion molecule-1 surface expression and soluble intercellular adhesion molecule-1 release may play an important role in interactions between lymphokine-activated killer cells and lung cancer cells.