1. A cotton wick probe has been used to measure the pressure in subcutaneous interstitial tissues of man.
2. The probe was inserted with minimal trauma into a plane of natural dissection at the level of the deep fascia in three sites: dorsum of the hand and foot, and the forearm.
3. The pressure was subatmospheric on every occasion (mean pressure: hand, −3·01 ± SD 0·50 cmH2O; foot, −3·54 ± SD 1·74 cmH2O; forearm, −2·41 ± SD 0·85 cmH2O).
4. Taking the three sites together, there was a positive correlation between wick pressure and locally measured tissue temperature (r = 0·55; P < 0·01), but when each site was analysed separately the relationship was significant only in the hand.
5. Wick pressure rose when the subcutaneous tissues were warmed.
6. A negative correlation was observed between wick pressure from the forearm and the subject's plasma colloid osmotic pressure (r = 0·73; P < 0·01), but no such relationship was observed in the hand or foot.