The purpose of this study was to examine the intra-tester and inter-tester reliability of strain gauge plethysmography (SGP) using the Hokanson EC-5R plethysmograph among three investigators. An arterial inflow test was performed by each of the investigators on fifteen college-aged volunteers at the forearm and calf sites. Intra-tester reliability was assessed by analyzing three serial measurements obtained at both sites. Intertester reliability was assessed in two ways: first, by having the three investigators obtain and analyze their own recordings, and, second, by having all three investigators (Testers 1, 2, and 3) analyze SGP recordings obtained by the most experienced investigator (Tester 1). The mean coefficient of variation (CV) for the intra-tester analysis was similar at the forearm (4.9%) and calf (4.0%) sites. The inter-tester analysis revealed that there were no significant differences among the three testers at either site when investigators obtained and analyzed their own waveforms. The CV calculated from the means of the three investigators was greater at the forearm site (10.7%) than at the calf site (2.5%). Similarly, when Testers 2 and 3 analyzed Tester 1's waveforms there were no significant differences found among testers at either site and the CV was less than when each investigator obtained his/her own waveforms. Strain gauge plethysmography blood flow measures obtained by experienced testers, under controlled laboratory conditions, are reproducible. The small variability in blood flow that exists is more attributable to variability in the acquisition of the waveforms than in the analysis of the waveforms.