Two instruments for laser Doppler fluxmetry were compared; a diode laser (Diodopp) with a He-Ne gas laser (Periflux Pf1d). Spatial variability during baseline registration and temporal variability during 3 standardized provocation tests (suprasystolic occlusion, tilting and inspiratory gasp) were evaluated in 20 healthy volunteers. The coefficient of variation (= CV) of the registrations on four adjacent places did not show any significant difference between both instruments. The biological zero obtained during 5 minutes vascular occlusion was always zero with the Diodopp and 4 (3-5) (median, [minimum-maximum]) Perfusion Units with the Periflux. The hyperaemic response measured by both instruments was less pronounced during the Diodopp registration (percentage LDF increase 173% (15-350) vs 354% (86-1100), p < 0.001). Although the CV of the LDF parameters obtained by the Diodopp during the standardized provocation tests was almost always lower then with the Periflux, only occasionally the differences reached statistical significance. We concluded that both laser Doppler instruments are of equal value. The reproducibility of the Diodopp is slightly better, but the hyperaemic response after occlusion is registrated in a different way by both instruments.