The ability of two plant materials, Cactus latifaria and the seeds of Prosopis juliflora, to act as natural coagulants was tested using a synthetic water formulated to resemble the drinking water supplied to the city of Maracaibo. Turbidity was added as kaolin. The coagulation ability of the two materials was assessed by the use of standard jar test measurements. Both materials produced comparable turbidity removals and were able to produce a final water whose turbidity was close to the required standard of 5NTU with both high (100-200 NTU) and low (30-40 NTU) initial turbidities. This was comparable with the performance achieved by previous workers using Moringa oleifera extracts. The optimum coagulant dose was found to be lower than that for aluminium sulphate. Treatment of the raw vegetable solids with solvents produced coagulants which, in some cases, were different from the raw materials and suggested that non-polar material might be involved with the coagulation process.