['To test if a small muscle injury influences the vascular reactivity to adrenaline in human skeletal muscle.', 'Blood flow was measured by ¹³³Xenon clearance in the gastrocnemius muscle of eight male subjects at basal and during i.v. infusion of adrenaline (0.1 nmol kg⁻¹ min⁻¹) or placebo. Measurements were done with (expts 2 and 3) or without (expt 1) the influence of a small muscle injury induced by inserting a microdialysis catheter. ¹³³Xenon was administered either (expt 1) conventionally into the muscle via a fine needle, or (expts 2 and 3) through a fine tube close to the inserted microdialysis catheter. Expt 3 (control expt) was identical to expt 2 except that placebo was infused instead of adrenaline. Mean ± SEM, n= 8.', '\u2002 The blood flow tended to increase during the adrenaline infusion in expt 1 (1.17 ± 0.10 to 1.39 ± 0.15, N.S.), whereas it decreased during the adrenaline infusion in expt 2, from 1.39 ± 0.14 to 1.03 ± 0.14 ml min⁻¹ 100 g tissue⁻¹ (P<0.001). The blood flow change in response to adrenaline infusion was significantly different in expt 1 and expt 2 (P<0.05). Blood flow also decreased during the placebo infusion in expt 3 (1.15 ± 0.10 to 1.00 ± 0.09, P<0.01), but this decrease was significantly smaller than in response to the adrenaline infusion in expt 2, P<0.01.'] Does intravenous adrenaline infusion cause vasoconstriction close to an intramuscular microdialysis catheter in humans?