Steady-state cellular water content and cation content and concentration have been studied in slices of rat renal cortex incubated in media in which Cl- was replaced by various monovalent anions at pH 7.35. Anions derived from low molecular weight aliphatic acids caused net uptake of cell water and K+. In the presence of larger anions cell water content fell in a manner related to anionic equivalent weight, but water content in media containing anions from weak aliphatic or alicyclic acids was slightly but consistently higher than that in media containing anions from strong acids. Cell K+ content did not decrease in these media. Aromatic anions caused enhanced cell water loss. When external pH adjusted to 6.8 or 7.8 it was found that in media containing anions from weak acids, but not from strong acids, increasing pH was associated with significantly decreased cell water content.