Despite the profound therapeutic and prognostic implications of nodal metastases in patients with melanoma, there is no consensus strategy for the optimal detection of metastases in sentinel lymph node biopsies. Traditional microscopic examination may be too crude to detect scattered, individual tumor cells. Conversely, molecular genetic techniques are prone to false-positive results. The authors evaluated the ability of HMB-45 immunohistochemistry to enhance detection of melanoma cells in histologically negative sentinel lymph nodes. Ninety-six sentinel lymph nodes, collected over a 25-month period from 66 consecutive patients with melanoma, were processed routinely and sectioned serially. Slides 1, 3, and 5 were stained with hematoxylin and eosin. HMB-45 staining was performed on an intervening slide in histologically negative nodes. To assess the background incidence of HMB-45-positive cells in lymph nodes draining the skin, the authors stained 244 cervical and axillary lymph nodes from patients without melanoma. Metastases were apparent microscopically in 12 (18%) of the 66 patients with melanoma. Of the remaining 54 patients, four patients (7%) had lymph nodes harboring individual, scattered HMB-45-positive cells. Benign nevocellular aggregates were present in four of the 96 sentinel lymph nodes (4% nodal incidence), but they were HMB-45-negative. The authors did not observe a single HMB-45-positive cell in the 244 lymph nodes from patients without melanoma. Immunohistochemistry appears to represent a specific means of enhancing tumor detection in sentinel lymph nodes from patients with melanoma.