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The use of advanced surface-analytical techniques t o study the sorption of the actinides uranium and plutonium on to rocks and their consistuent minerals, in the context of radioactive waste disposal, is described. Nuclear microprobe analysis was used t o quantify the extent of sorption of actinides via Rutherford back-scattering (RBS); data on the minerals o n which sorption had occurred were provided by particleinduced X-ray emission. Both surface and su b-surface concentrations of actinides were measurable. Secondary-ion mass spectrometry (SIMS) was used to measure qualitatively the distribution of sorbed actinides and their penetration rates into minerals. The equipment used at Harwell is described. Complementary use of both techniques in parallel is highly advantageous; RBS is used to quantify actinide surface loadings, w i t h limited lateral and depth resolution, but, allied to SIMS, which has excellent spatial resolution, samples can be analysed both quantitatively and with high spatial resolution. Concentrations of uranium and plutonium sorbed o n t o minerals can be routinely determined w i t h sensitivities d o w n to 1 ng cm-*. The data obtained are used to identify the minerals in a rock that are important for actinide sorption.