AbstractEighteen patients with advanced non‐small‐cell lung cancer (NSCLC) received recombinant beta interferon, 90 million units three times weekly. No complete or partial responses were seen. Five patients had stable disease for several months. Most patients experienced some toxicity, most commonly fever and chills. No dose reduction of interferon had to be made due to toxicity. Tachyphylaxis to symptoms of fever and chills occurred in most patients. While 33% of patients developed beta‐interferon‐binding antibodies, the incidence of interferon‐neutralizing activity was 0%. This dose and schedule of beta interferon did not result in significant anti‐tumor effects in advanced NSCLC. Stabilization of disease for up to 9 months in patients with previously progressive disease was of interest. Tachyphylaxis of symptoms should allow for dose escalation within patients. A dose‐escalating study has been initiated to evaluate the efficacy of beta interferon when given at each patient's maximally t