The present study has been performed to elucidate a possible role of cell volume in low-density lipoprotein (LDL) binding and internalization (LDL_b+i). As shown previously, increase of extracellular osmolarity (OSMe) and K⁺ depletion, both known to shrink cells, interfere with the formation of clathrin-coated pits and thus with LDL_b+i. On the other hand, alterations of cell volume have been shown to modify lysosomal pH, which is a determinant of LDL_b+i. LDL_b+i have been estimated from heparin-releasable (binding) or heparin-insensitive (internalization) uptake of ¹²⁵I-labeled LDL. OSMe was modified by alterations of extracellular concentrations of ions, glucose, urea, or raffinose. When OSMe was altered by varying NaCl concentrations, LDL_b+i decreased (by 0.5 ± 0.1%/mM) with increasing OSMe and LDL_b+i increased (by 1.2 ± 0.1%/mM) with decreasing OSMe, an effect mainly due to altered affinity; the estimated dissociation constant amounted to 20.6, 48.6, and 131.6 µg/ml at 219, 293, and 435 mosM, respectively. A 25% increase of OSMe increased cytosolic (by 0.46 ± 0.03) and decreased lysosomal (by 0.14 ± 0.02) pH. Conversely, a 25% decrease of OSMe decreased cytosolic (by 0.28 ± 0.02) and increased lysosomal (by 0.17 ± 0.02) pH. Partial replacement of extracellular Na⁺ with K⁺ had little effect on LDL_b+i, although it swelled hepatocytes and increased lysosomal and cytosolic pH. Hypertonic glucose, urea, or raffinose did not exert similar effects despite a shrinking effect of hypertonic raffinose. Monensin, which completely dissipates lysosomal acidity, virtually abolished LDL_b+i. In conclusion, the observations reveal a significant effect of ionic strength on LDL_b+i. The effect is, however, not likely to be mediated by alterations of cell volume or alterations of lysosomal pH.