Seventy Syrian golden hamsters bearing SC transplants of Greene melanoma were used to evaluate the degree of tumour uptake of several 11C-radiopharmaceuticals selected for their potential specificity for melanoma. Tissue distribution studies were performed at 30 and 60 min after IV injection of 11C-compounds and compared with the 24-h uptake of 67Ga-citrate. Gamma camera images were also compared. The highest tumour uptake at 1 h was observed with 11C-methionine (2.42% +/- 0.72%) and although activity in liver, spleen and kidney exceeded that in melanoma the tumour was demonstrated on gamma camera imaging. Melanoma localisation of 11C-chlorpromazine, 11C-flunitrazepam and 11C-ketanserine was comparable at 1% of the dose injected per gram of tumour. High activity in other organs, particularly liver, exceeded uptake in melanoma and attempts at tumour imaging were unsuccessful. Tumour accumulation of 11C-methiodide quinuclidinyl benzylate (MQNB), an 11C-imidazobenzodiazepine (Ro-15-1788) and 14C-pimozide was low and imaging studies were not attempted. None of the 11C-radiopharmaceuticals evaluated for melanoma affinity matched that of 67Ga-citrate. The 24-h tumour uptake of 67Ga-citrate was 4.07% +/- 1.37% dose injected per gram which allowed delineation of the melanoma by gamma camera imaging.