1010-cycle fatigue tests were conducted at 100 Hz for three years and at 20 kHz for one week on 1800 MPa-class JIS-SUP7 spring steel. Uniaxial tests up to 108 cycles were also conducted at 120 and 600 Hz. The 120 Hz tests had larger control volumes. The fatigue limit at 1010 cycles was lower than at 108 cycles, and any frequency effect was shown to be negligible. A size effect was found; the tests with larger control volumes showed results of lower fatigue strength.