The analgesic efficacy of intravenous doses of acetaminophen (paracetamol) 0.5 g, 1 g and 2 g (administered as propacetamol) was assessed in 11 healthy subjects in a randomised, double-blind, placebo-controlled crossover study. The antinociceptive effect was assessed over 8 h by measurement of the nociceptive flexion reflex threshold (R-III) in response to selective transcutaneous electrical stimulations.