In Ehrlich mouse ascites tumour cells, exposed intra-abdominally to [2-³H]inositol, ATP and GTP presented enough aberrant ³H-label to cause potential interference in the chromatographic analysis of inositol phosphates involved in signal transduction. After acid extraction and charcoal adsorption/desorption the nucleotides were dephosphorylated, enriched with [U-¹⁴C]adenosine, and exposed to purine-nucleoside specific enzymes. Reverse phase HPLC and radioactivity measurement demonstrated that for adenosine about 82% of total stable ³H label was in ribose and thus about 18% in adenine. For guanosine about 89% was in ribose and 11% in guanine. This aberrant ³H labelling could be avoided using [1-³H]inositol. Copyright © 2000 John Wiley & Sons, Ltd.