Ninety-two percent of the intense magnetic fields (>13 &ggr;) observed at 1 AU During solar cycle 20 (1963--1975) were associated with shocks, stream interfaces, or cold magnetic enhancements (CMF's). Most (52%) of the magnetic field intensity enhancements occurred at stream interfaces; 27% occurred behind shocks without interfaces; and 11% occurred in CME's. The most intense fields (25--37 &ggr;) followed shocks. Magnetic field intensities at interfaces did not exceed 25 &ggr;, suggesting that some mechanism limits the intensity ahead of steams. During the period 1973--1975, interface-associated enhancements occurred 3.5 times as frequently as shock-associated enhancements, and during an earlier period (1967--1969) when the sun was more active, shock-associated enhancements occurred 1.2 times as frequently as interface-associated enhancements. The frequency of CME's was the same in both periods. The absolute occurrence frequency of interface-associated enhancements increased by a factor of 2.4 in going from the early period to the later period, while the absolute occurrence frequency of shock-associated enhancements decreased by a factor of 1.7 in going from the early to the late period.