AbstractThe radioactive melanin used in this study was extracted from the cell walls of the fungus Aspergillus nidulans after growth in the presence of14C‐labelled precursors. The counting systems investigated comprised solid samples suspended in a liquid scintillator with or without silica gel, solubilized samples blended in a liquid scintillator and solubilized samples adsorbed on to glass‐fibre discs wich were suspended in a liquid scintillator. Results obtained by counting solid samples with an end window detector are compared with the liquid scintillation data. High counting efficiencies were realized with the glass‐fibre disc method which is recommended for the assay of soluble samples. Liquid scintillation counting of silica gel suspensions was vastly superior to end window counting for the assay of solid samples. The data suggest that14C‐labelled materials of a particulate or highly pigmented nature can be counted with high efficiency in a liquid scintillation