Metabolic activity of both NIH 3T3 (A, B) and SH-SY5Y cells (C, D) grown in culture medium containing 6.4 (Pos.Ctrl., reference), 6.26, 6.12 and 5.93 mg/ml NaCl corresponding to 1:10, 1:5 and 1:3 dilution of the NaCl stock in culture medium was determined by indirect reduction of WST-1 by mitochondrial dehydrogenases to a formazan dye. Optical densities (OD) were measured in 48 h and 6 d cultivation assays (NIH 3T3, n = 13–23; SH-SY5Y, n = 24–27). The resulting formazan dye intensities were also related to those obtained from the reference and calculated as a percentage [%]. Each data point is presented as mean and SEM. ANOVA with Newman-Keuls multiple comparison test was performed for statistical assessment (***p ≤ 0.001, *p ≤ 0.05).