An example is shown how pulse radiolysis conductivity measurements are affected by the addition of buffer. The latter reduces the measurable conductivity changes within the region of several pH units near the p Ka of the buffer. The resulting conductivity-pH curves are not identical, however, with the thermodynamic p K curve of the buffer. The position of these curves is rather dependent on the buffer concentration. In the investigated system (R 2S∴ SR 2+ radical cation formation in the OH radical induced oxidation of R 2S, and addition of acetic acid/acetate buffer) they are increasingly shifted towards lower pH and also become increasingly steeper with increasing buffer concentration. The apparent "p K" values are found to be 4.29, 3.88, 3.75 and 3.34 for 1 × 10 -4, 5 × 10 -4, 1 × 10 -3 and 5 × 10 -3 mol dm -3 buffer, respectively. The experimental results agree with theoritically calculated data.