Accurate staging of patients with primary cutaneous melanoma includes assessment of regional lymph nodes for the presence of micrometastatic disease. Sentinel lymph node biopsy is highly accurate but is an invasive surgical procedure with a 5-10% complication rate, and requires labour-intensive and expensive histological examination to identify disease. A rapid, accurate and cost-effective non-surgical technique able to detect micrometastatic deposits of melanoma in regional lymph nodes would be of great benefit. Fine needle aspiration biopsies and tissue specimens were obtained from lymph nodes from 18 patients undergoing node resection for metastatic melanoma and five patients undergoing radical retropubic prostatectomy. One-dimensional proton magnetic resonance spectroscopy was undertaken at 360 MHz (8.5 T). Lymph nodes were cut into 3 mm thick slices and embedded. Four sequential 5 microm tissue sections were cut from each block and stained, with haematoxylin and eosin, for S100 protein, for HMB45, and again with haematoxylin and eosin, respectively. Proton magnetic resonance spectroscopy distinguished between benign and malignant lymph node tissue (P < 0.001, separate t-test) and benign and malignant lymph node fine needle aspiration biopsy (P < 0.012) based on the ratio of the integrals of resonances from lipid/other metabolites (1.8-2.5 p.p.m. region) and 'choline' (3.1-3.3 p.p.m. region). In conclusion, one-dimensional proton magnetic resonance spectroscopy on a simple fine needle aspiration biopsy can distinguish lymph nodes containing metastatic melanoma from uninvolved nodes, providing a rapid, accurate and cost-effective non-surgical technique to assess regional lymph nodes in patients with melanoma.