An experiment was conducted to study the efficacy of two tomato pastes and aronia nectar (fruit juice + pulp from the black chokeberry, Aronia melanocarpa Elliot) as inhibitors of nitrosamine production in cancer prophylaxis programmes. White male rats of the Wistar strain were employed in an acute trial. Aminopyrin+sodium nitrite (APSN) were used as precursors for generation of endogenous nitrosamine. The animals were allocated to different dietary groups and fed by intubation with APSN or APSN + food products. Introduction of tomato paste (TP), high-beta-carotene tomato paste (HCTP) and aronia nectar (AN) as inhibitors of N-nitrosamine formation exerted a positive effect on blood and liver variables which was demonstrated by decreased concentrations of glutamic-oxaloacetic transaminase (EC 2.6.1.1), glutamic-pyruvic transaminase (EC 2.6.1.2) and uric acid in serum and lipid content in hepatocytes. Animals treated with APSN developed dystrophic changes in liver such as centrolobular necrosis, intense exangia, and enlarged cells with two, often large, pyknotic nuclei, while the structure of livers of rats fed with TP, HCTP or AN was well protected and almost normal. TP had a particularly beneficial effect on serum total protein and albumin concentrations as had AN on the urea value. The inhibitory effect of the food products used is explained by their chemical nature including pH, ascorbic index (ascorbate:nitrate), lycopene and beta-carotene contents.