Sodium nitrite ($NaNO_2$) is a precursor to a variety of organic compounds (pharmaceuticals, dyes and pesticides), but it is best known as a food additive. The aim of the study is to investigate the influence of acute (i.p.) treatment of Wistar rats with $NaNO_2$ (at the dose of 50 mg/kg b.w.) on the blood rheological properties and erythrocyte hematometric indices (Hb, HCT, RBC, MCV, RDW, MCH, MCHC). The significant differences were not found in the whole blood viscosity (WBV) values of the control and $NaNO_2$-treated groups. The changes in the erythrocyte hematometric indices were statistically significant for RDW, MCHC and MCH at the $1^{st}$ hour, five- and ten days after $NaNO_2$ administration. Interestingly, at the day $5^{th}$ of the $NaNO_2$ treatment we obtained statistically significant lower values for the RBC count, Hb, HCT, RDW, as well as elevated indices MCV (no statistically significant), MCH, MCHC. The results obtained indicate that hemorheological and hematometric parameters examined should be monitored in cases of acute exposure to nitrites - for the purposes of clinical toxicology. The quantitative values of hematometric indices reported in our experimental model could be suitable for predicting $NaNO_2$ intoxication and methemoglobinemia in animals and humans.