INTRODUCTION: In this study, we examined whether epidermal growth factor receptor (EGFR) mutations were detectable using a polymerase chain reaction-based assay and wash fluid of computed tomography (CT)-guided lung biopsy needles. METHODS: DNA was extracted from wash fluid of CT-guided biopsy needles of 53 lung tumors (as diagnosed according to the results of the CT-guided biopsies). EGFR mutations, specifically exon19 deletions and exon21 L858R mutations, were examined using a mutant-enriched polymerase chain reaction assay. We also examined the presence of EGFR mutations in 26 surgically resected tumor specimens and compared the results with those obtained for the corresponding wash fluid samples. RESULTS: The amount of DNA obtained for the wash fluid of the CT-guided biopsy needles ranged from 35 to 2360 ng. There were no significant differences in the amount of extracted DNA according to the tumor characteristics, including tumor size and the percentage of ground glass opacity. Thirty-four of the 53 lung tumor samples were histologically diagnosed as non-small cell lung cancer (NSCLC). Exon19 deletions and exon21 L858R mutations in EGFR were detected in 4 (12%) and 13 (38%) of 34 NSCLC cases, respectively. No EGFR mutations were found in the non-NSCLC cases. The EGFR mutation status in the wash fluid samples was consistent with those obtained for all 26 corresponding surgical specimens. CONCLUSION: Our results indicate that EGFR mutations can be detected using wash fluid of CT-guided biopsy needles. In this manner, the DNA genotype can be determined even in extremely small clinical specimens using highly sensitive assays.