1. The local responses to intradermal injection of PAF, histamine and PGE2 were investigated in eight healthy male volunteers. Acute effects were monitored by weal and flare measurement; delayed effects were investigated by pain threshold testing and skinfold thickness measurements. 2. PAF and PGE2 were found to induce weal and flare responses which were clearly distinguishable from vehicle and dose related. 3. PAF was approximately 50 times as potent as PGE2 at inducing weal on a molar basis. 4. A dose related hyperalgesia was recorded in response to PGE2. No hyperalgesia could be demonstrated following PAF injection compared with vehicle. 5. PAF and histamine elicited an increase in skinfold thickness up to 2 h after injection which was distinguishable from vehicle.