Sentinel node (SN) biopsy is a staging technique used to select patients for regional lymphadenectomy in melanoma. We compared the two most widely used radioactive tracers, 99mTc-colloidal albumin (99mTc-CA) and 99mTc-sulphur colloid (99mTc-SC), with respect to scintigraphy, success rate in gamma probe guided biopsy and absolute uptake in the SN. Scintigraphy was performed in six volunteers after simultaneous injection of the respective tracers in each leg. Comparison of uptake of both tracers showed a higher uptake on the 99mTc-CA side. The scintigraphic count ratio of SNs labelled with 99mTc-SC compared with 99mTc-CA was 1 to 9-28. Next, 20 patients with biopsy-proven melanoma were randomized for injection of 99mTc-CA or 99mTc-SC followed by SN biopsy. Within 20 min after the injection, focal uptake was seen in all cases of the 99mTc-CA group but in only seven of the 10 patients in the 99mTc-SC group (P<0.05). Focal accumulations were seen in all patients of both groups after 2 h. Spill to non-SNs was seen in five of the 99mTc-CA patients and three of the 99mTc-SC patients. In all patients the SNs could be retrieved under the guidance of a gamma probe and blue dye. The uptake in the SN was significantly higher (P<0.001) after the injection of 99mTc- CA (0.92 ± 0.40%) compared with 99mTc-SC (0.34 ± 0.34%). When dynamic scintigraphy is performed, 99mTc-CA is preferable. SN uptake of 99mTc-SC is less than that of 99mTc-CA but this does not adversely affect the surgical procedure.