A continuing study of possible impact of extreme low-frequency electromagnetic fields (Sanguine effect) on soil arthropods was enlarged in summer 1972 to include 11 test plots and six control plots. This report analyzes mite and collembolan populations in plots that have been under investigation for at least two years. New plots, initially sampled in 1972, will be sampled again in summer 1973 to provide a time dimension, and they will be reported on subsequently. These annual censuses provide data on within-year and between-year population changes of soil microarthropods in various habitats. As in 1971, no significant differences occurred between each of four groups of arthropods in the Main test and control subplots. In 1972, statistically significant differences were observed among the microfauna in some of the other plots that were absent in 1971. In some cases the density of a group was greater in the control plot; in other cases, the density was greater in the test plot. A general feature of the population curves of all groups in test and control plots is the midsummer peak with return to spring levels by mid-September. Within-plot peak amplitude varies from one year to the next, and both chronicity and amplitude appear to be independent of a Sanguine effect and are attributable to random, natural causes. Consequently, variations in absolute numbers are less reliable than intergroup ratios and annual population curves as evidence for significant population shifts. Four-year ratios of Cryptostigmata: Collembola in Hazleton plots disclose that populations of these two most numerous groups of decomposers are remarkably parallel in test and control plots. Numerous other examples are given of between-year populational changes which, because they occur in test and control plots alike, rule out a Sanguine effect.