A new range of sulfided iron catalysts has been synthesised by adding small amounts of Na2S (500-20 000 ppm) to precipitated iron. The new materials, after calcination (400 degrees C, 16 h) and reduction (400 degrees C 16 h), were subjected to syngas (2 : 1 H-2 : CO) at 250 degrees C at 8 bar pressure for up to 8 days. Catalysts with low sulfide concentrations were up to four times more active in the Fischer-Tropsch reaction than a sulfur-free catalyst, while catalysts with high sulfide loadings were apparently poisoned. Increased olefin/paraffin ratios were also obtained at the low sulfide loadings. The new sulfided materials were studied by a combination of BET, DRIFTS, XRD, TPR and SEM and the results indicate that the surface area and reducibility of the iron catalyst are affected by the presence of S2- ions and that SO42- acts as a promoter in the Fischer-Tropsch reaction.