In this study we assessed the effects of changes in pH, temperature, and their combination in whole blood on thromboelastographic variables. Blood was collected from six healthy volunteers. Thromboelastograph (TEG series 5000; Haemoscope Corporation, Illinois, USA) channels were set at temperatures of 32, 37, and 39°C and each was filled with artificially acidified, alkalified, and neutral blood, respectively. Acidification (pH 6.95) significantly impairs thromboelastographic variables reaction time r (from 23.3 to 33.7 min; P = 0.0280), kinetic time k (from 8.7 to 16.1 min; P = 0.028), angle α (from 24.3° to 13.8°; P = 0.028), prothrombin time (from 11.4 to 12.1 s; P = 0.044), and activated partial thromboplastin time (from 29.3 to 45.0 s; P = 0.028). A temperature drop from 37 to 32°C in blood of neutral pH significantly impaired k (from 8.7 to 10.2 min; P = 0.028) and α (from 24.3° to 21.0°; P = 0.027), whereas maximum amplitude ma significantly increased (from 46.5 to 52.5 mm; P = 0.027). A temperature rise from 37 to 39°C at pH 7.37 did not affect any of the TEG variables. Artificial alkalization (pH 7.68) at a temperature of 37°C had no effect on any of the measured variables. Acidosis causes a significant impairment of clot formation and clot strength. Hypothermia had the same effects, but to a lesser extent. These findings emphasize the need for correction of acidosis and hypothermia to normalize haemostasis.