The efficacy, tolerability and immunomodulatory effects of CGP 19835A Lipid, a liposomal preparation containing a lipophilic derivative of muramyltripeptide, a drug experimentally known as a potent activator of the macrophage-monocyte system, were evaluated in patients with advanced non-small-cell lung cancer (NSCLC). The immunomodulator was administered intravenously weekly to 12 patients in 3 different dosages: 4mg (n = 4), 2mg (n = 5), and 1mg (n = 3). Adverse events suggesting macrophage activation were observed in almost all patients, despite the dosage used, and included fever, chills, asthenia, anorexia and weight loss. Serum levels of tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), neopterin, C-reactive protein and soluble IL-2 receptors were increased in accordance with clinical side effects. No objective antitumoral effect was observed in patients with bulky NSCLC. When given to these patients, CGP 19835A Lipid appeared to be effective in increasing serum TNF-α levels. This property could be investigated in order to potentiate anticancer chemotherapy.