The relative importance of pH, diprotonated phosphate (H2PO4-) and potassium (K+) for the reflex increase in mean arterial pressure (MAP) during exercise was evaluated in seven subjects during rhythmic handgrip at 15 and 30% maximal voluntary contraction (MVC), followed by post-exercise muscle ischaemia (PEMI). During 15% MVC, MAP rose from 92 +/- 1 to 103 +/- 2 mmHg, [K+] from 4.1 +/- 0.1 to 5.1 +/- 0.1 mmol L-1, while the intracellular (7.00 +/- 0.01 to 6.80 +/- 0.06) and venous pH fell (7.39 +/- 0.01 to 7.30 +/- 0.01) (P <0.05). The intracellular [H2PO4-] increased 8.4 +/- 2 mmol kg-1 and the venous [H2PO4-] from 0.14 +/- 0.01 to 0.16 +/- 0.01 mmol L-1 (P <0.05). During PEMI, MAP remained elevated along with the intracellular [H2PO4-] as well as a low intracellular and venous pH. However, venous [K+] and [H2PO4-] returned to the level at rest. During 30% MVC handgrip, MAP rose to 130 +/- 3 mmHg, [K+] to 5.8 +/- 0.2 mmol L-1, the intracellular and extracellular [H2PO4-] by 20 +/- 5 mmol kg-1 and to 0.20 +/- 0.02 mmol L-1, respectively, while the intracellular (6.33 +/- 0.06) and venous pH fell (7.23 +/- 0.02) (P <0.05). During post-exercise muscle ischaemia all variables remained close to the exercise levels. Analysis of each variable as a predictor of blood pressure indicated that only the intracellular pH and diprotonated phosphate were linked to the reflex elevation of blood pressure during handgrip.