The purpose of the study was to investigate with what accuracy the soleus H-reflex modulation and excitability could be measured during human walking on two occasions separated by days. The maximal M-wave (Mmax) was measured at rest in the standing position. During treadmill walking every stimulus elicited an M-wave of 25+/-10% of Mmax in the soleus muscle and a supra-maximal stimulus elicited a maximal M-wave 60ms after the first stimulus. Both Mmax during rest and during walking were later used for normalization. When normalized to resting Mmax, the peak reflex amplitude during walking was 5% lower on Day 2 than on Day 1 (p=.32). However, when the peak H-reflex was normalized to Mmax in every sweep, Day 2 showed a significant 15% lower amplitude (p=.037). The same pattern was found for the mean H-reflex. Spearman's Rho was .92 when normalized to resting Mmax but .88 when normalized to Mmax in every sweep. The Pearson product was used to identify one participant at a time on Day 1 among all seven participants on Day 2. For both normalization procedures 5 of 7 participants were identified by this test. Since 5 of 7 participants were recognized between days, it must be recommended to use 10-15 participants for training or intervention studies as far as the H-reflex pattern of modulation during movement is concerned.