1. Hepatic intracellular pH (pHi) was measured in intact rats by distribution of 5,5-dimethyloxazolidine-2,4-dione (DMO), using [14C]DMO and a range of doses of unlabelled DMO, previously neutralized with sodium hydroxide.
2. Mean calculated pH; fell from 7·27 to 7·17 as the dose of added unlabelled DMO was increased from zero to 0·19 mmol/kg (25 mg/kg) and thereafter remained constant up to and including the highest dose group (1·55 mmol/kg; 200 mg/kg).
3. Control observations showed that the change in calculated pHi with DMO dose could have been related to the consequential sodium load, rather than to the presence of a saturable process determining the distribution of DMO.
4. Reasons are given why it is nevertheless desirable to add carrier DMO when employing [14C]DMO for the measurement of hepatic pHi in the rat.