Under the influence of such low amounts of fluorine, the number of actinomyces and the activity of urease increased in soil tested after the harvest of winter rape and yellow lupine, the latter being a catch crop sown after maize. The neutralizing substances had a much better effect on counts of the analyzed microorganisms than on the activity of soil enzymes. The counts of actinomyces and copitrophic bacteria were positively affected by all the substances added to soil, as compared to the control treatments. With respect to fungi, these microorganisms responded positively only to the application of charcoal and loam to soil cropped with yellow lupine.