We studied the effects of a micro-Tesla extremely low frequency magnetic field (microT ELFMF) on blood pressure. A 1-muT magnetic field was generated by Helmholtz coils (L, 3.0 meters; H, 1.7 meters) with 8/6-Hz alternating current. This study was carried out between March 2004 and March 2005, and data from a total of 30 volunteers were analyzed. The subjects' blood pressure was measured before and after exposure, at baseline, and 1, 2 and 3 months after the first ELFMF session. The mean age of the subjects was 46.5 years (range, 28-72 years). The median number of ELFMF sessions was 31.5, and the median duration of each session was 10.0 min (range, 2.0-120.0 minutes). In the hypertensive and normotensive subgroups, the difference between the baseline and 3-month pre-exposure systolic blood pressure (SBP) measurements was statistically significant (p<0.001, p=0.013, respectively; paired t-test). The SBP of the hypertensive subgroup decreased more than that of the normotensive subgroup. These data suggest that the microT ELFMF may have a hypotensive effect on subjects, particularly hypertensive subjects.