The purpose of this study was to find out whether hypokalaemia and associated ECG changes occur as a result of field block for hernial repair, alone or in combination with surgery. We recorded the ECG and measured the serum potassium and the plasma catecholamine concentrations at 10-min intervals in three groups of patients. In Group 1 (n = 7) and in Group 2 (n = 7), the blockade was instituted with prilocaine 0.5% and adrenaline 1:250,000, while in Group 3 plain prilocaine 0.5% was used. In Group 1 surgery was withheld for 40 min, while in Groups 2 and 3 surgery started as soon as the blockade became effective. There was a prolonged 4 to 5-fold elevation of the plasma adrenaline level from the adrenaline-containing solutions, the peak being 2.44 +/- 0.48 nmol/l (mean +/- s.d.) 10 min after the blockade had been instituted. The S-K level was unchanged in Group 1, while in Group 2 it decreased from 4.14 +/- 0.33 mmol/l to 3.91 +/- 0.29 at 60 min (P less than 0.05). An ECG pattern consistent with hypokalaemia did not develop. In Group 3, with plain prilocaine, there was a significant increase in the S-K level from 3.86 +/- 0.21 mmol/l to 4.08 +/- 0.36 at 40 min (P less than 0.05).