Microdialysis enables in-depth mechanistic study of the cutaneous circulation in humans. However, whether the insertion or presence of the microdialysis fiber (MDF) affects the skin circulation or its responses is unknown. We tested whether the cutaneous vascular response to whole body heating (WBH) was affected by MDF or by pretreatment with ice (Part 1) or local anesthesia (LA; Part 2). Nine subjects participated in Part 1 and eight in Part 2. In both parts, 4 sites on the forearm were selected; providing untreated control, MDF only, ice or LA only, and combined MDF plus ice or LA. A tube-lined suit controlled whole body temperature, which was raised to ~38° for WBH. Skin sites were instrumented with laser-Doppler flow probes. Data were expressed as cutaneous vascular conductance (CVC). Baseline levels were not different among sites (P>0.05). In Part 1, the internal temperature for the onset of vasodilation was higher (P>0.05) with MDF with or without ice pretreatment than at untreated control sites. Peak CVC during WBH was decreased (P<0.05) by MDF (control 73±7%max, MDF 60±6%max). Ice or Ice+MDF did not affect (P>0.05) peak CVC compared to control. In Part 2, the temperature threshold for the onset of vasodilation was increased by MDF with or without LA treatment and by LA alone (P<0.05). Peak CVC was decreased by MDF (control 69±6%max vs. MDF 58±8%max; P<0.05). LA only (65±10%max) or MDF in the presence of LA (73±12%max) did not affect (P>0.05) peak CVC compared to control. Thus, LA or MDF increases the temperature threshold for the onset of vasodilation. MDF alone decreases the peak vasodilator response in CVC to WBH, but, this attenuation did not occur if ice or LA is used before MDF placement. Ice or LA alone do not affect the peak response in CVC to WBH.