The hydrogenation of CO to hydrocarbons is investigated over zirconia iron-based catalysts prepared by co-precipitation. These catalysts, in which the Fe-content varied between 0 and 100 %, were tested in the CO hydrogenation reaction under fixed reaction conditions (H-2/CO = 2, T = 250 A degrees C, P = 20 bar, GHSV = 0.0083 L/g.s.). The resulting activity data indicated that CO conversion is strongly dependent on the iron contents of the catalysts. The lowest CO conversion (< 5 %) was obtained using Zr-rich catalysts (15Fe and 5Fe), and the highest CO conversion was obtained using Zr-free (100Fe) catalysts. For this catalyst, the CO conversion level reaches 38.5 %, with selectivities for the C-2-C-4 and C-5+ hydrocarbons of 49.7 and 27.7 %, respectively. However, the activity profile of this catalyst slightly decreases with the time on-stream, indicating that it is progressively deactivated. If the activity is normalized to the iron content, the 95Fe and 85Fe catalysts display slightly better performances and are relatively stable for on stream periods of at least 48 h. [GRAPHICS] .