Sentinel lymph nodes provide an excellent opportunity to study early immune responses to cancer. However, harvesting live cells has not previously been possible, because it conflicts with the need to preserve tissue for histological interpretation. This study used scrape cytology on 26 sentinel and 8 non-sentinel nodes, harvested from 17 stage I/II melanoma patients undergoing sentinel node biopsy. Numbers of viable cells harvested before and after cryopreservation were measured and the effect on subsequent histology assessed. The mean number of cells harvested from 26 sentinel nodes was 7.06 x 10(6) (range 0.1-32.2), with a mean viability of 99.5% (range 87-100, lower 95% CI 98.5%). Furthermore, counts and viabilities were well maintained after cryopreservation. Flow cytometry confirmed CD3+, CD20+ and lineage-1-/HLA-DR+ subpopulations, consistent with T-lymphocytes, B-lymphocytes and dendritic cells, respectively. Importantly, there was no discernible change in histological detail and the proportion of positive sentinel nodes remained unchanged. This technique will allow more functional and quantitative approaches to sentinel lymph node research.