During a survey on the occurrence of pale, soft and exudative (PSE) pork at two abattoirs, pH readings taken at 30 and 45 min. post mortem in the M. semimembranosus differed significantly (P <0,01). At Abattoir A (electric stunning) the difference was 0,07 pH units and Abattoir B (captive bolt stunning) the difference was 0,20 pH units. At 45 min. post mortem muscles with a pH value of 6,0 and lower are characterised by typical PSE symptoms. The mean pH1 value (45 min. post mortem) was 6,41 at Abattoir A and 5,88 at Abattoir B (P < 0,01). The occurrence of PSE carcasses at Abattoir A was 12,92% and 71,92% at Abattoir B (P<0,01). Violent muscle contractions resulting from stunning by captive bolt pistol were responsible for the low pH1 values at Abattoir B.