Erlotinib potentiates antibody dependent cell cytotoxicity. The indicated human NSCLC cell lines were treated with 1 μM erlotinib for 24 h. After the treatment with erlotinib, 10 μg/ml Cetuximab (A, B, E) or Trastuzumab (C, D) were added to cancer cells seeded with 100 U/ml IL-2 activated-NK cells at the ratio of 1:25 and 1:50. After 4 h LDH release was determined as described in Methods section. The results are from representative experiments. The experiment, repeated three times, yielded similar results (**P < 0.01 ***P < 0.001).