A method for the determination of lead in slurries of marine sediment using palladium–magnesium nitrate as a chemical modifier has been optimized. To stabilize the marine sediment slurry, different thickening agents were studied. The grinding time and the particle size were also studied. To achieve complete pyrolysis of the slurry sample, two charring steps were used: the first one at a low temperature, 480 °C, and the second at 900 °C. The precision of the method was studied as within-run and within-batch precision; the relative standard deviations obtained in both cases were less than 3%. The relative standard deviation for the repeatability of the over-all procedure was 5.0%. The accuracy of the method was studied using a Certified Reference Material PACS-1 (Marine Sediment) from the National Research Council of Canada, which has a certified lead content of 404 ± 20 mg kg^–1; the result obtained was 418 ± 11 mg kg^–1. The detection limit for lead was 0.22 µg l^–1. Calibrations using aqueous standards and the reference material were compared. This method has been applied to the determination of lead in marine sediment samples from the Galicia Coast and the results were compared with a sample digestion method using nitric and hydrochloric acids in a high pressure poly(tetrafluoroethylene) bomb and microwave energy. No significant differences were found between the two procedures.