The aim of this study was to assess the cytotoxicity of tow types of impression dental materials: polyethers (Impregum Penta, Permadyne Penta Heavy and Light) and vinyl polysiloxanes (Elite Mono Tray, Medium, Low viscosity and Elite H-D Putty). Their cytotoxic effects were studied by indirect and direct tests. The indirect tests were performed by incubating impression materials in serum free cell culture medium to prepare the soluble extracts. Balb/c 3T3 cells were incubated with extract dilutions (25, 50, 75 and 100%) for 24 h. The extracts of polyether materials caused a decrease of cellular viability, evaluated by light microscopy, by cell counting and by MTT test. The extracts of vinyl polysiloxanes materials induced a slight effect on cellular number and viability. The direct tests were performed by placing the impression materials in the centre of Petri dishes while Balb/c 3T3 were settling. The cellular proliferation was drastically reduced by polyethers and it was unaffected by the presence of vinyl polysiloxanes. These results show that: (a) the polyether materials are more toxic than vinyl polysiloxanes in our experimental conditions, (b) the impression materials are cytotoxic to the same degree in all assay methods.