A rapid, inexpensive, colorimetric screening method for mercury (Hg) has been optimised to provide a semi-quantitative measurement of Hg concentration in marine sediment within the range 0.038 to 1.5 mg kg-1 encompassing the interim sediment quality guideline (ISQG) value of 0.13 mg kg-1 (CCME 1999) and the probable effects level (PEL) of 0.7 mg kg-1 for Hg in marine sediment (CCME 1999). Neither salinity (up to 41 practical salinity units (psu)) nor sediment organic matter (ΟΜ) content (up to 10%) affected the performance of the method. Accurate results were obtained for spike recovery experiments and analysis of certified reference material (CRM) BCR 580 Estuarine Sediment. The method was applied to sediment samples from Elefsina Bay, Greece. Screening results indicated Hg contamination in the bay, with concentrations exceeding the PEL value. Findings were confirmed by quantitative analysis of the samples by cold vapour atomic absorption spectrometry (CV-AAS), where results in the range 1.4–2.96 mg kg-1 were determined.