Rats initially weighing 138 +/- 14 g were fed the following diets for 150 days: control (Co), control plus nitrite-bacon-proline 24 mg/kg, 100 g/kg and 10 mg/kg, respectively (NB), NB plus 0.04 micrograms/g selenium (NBSe) and NB plus 0.020 g/kg ascorbic acid (NBC). The NB diet provoked body weight and feeding efficiency enhancement with a reduction in body density increasing serum lactic acid, uric acid and cholesterol levels. The serum selenium decreased by the presence of NB in the diet. The addition of selenium and ascorbic acid to the NB diet prevented the reduction in body density and also affected uric acid and cholesterol levels. It is suggested that the NB diet has adverse effects and that some of the alterations it causes are prevented by the reducing elements selenium and ascorbic acid.