One of the  bioindicators  most often applied  to assess  the  quality  of soil  is its enzymatic  activity.  Undesirable changes  in  the  activity  of enzymes  can imply excessive  presence of substances   which  are  harmful to  soil environment,  such as  heavy  metals.   Being  a  heavy  metal,  zinc  is  also an  element  essential for maintaining proper  functions  of live  organisms. The purpose of this study has been to determine  the  significance of changes occurring  in moderately heavy  soil  under  the  influence  of zinc. The experiment   was  carried  out  in three  replicates   under  laboratory  conditions.  Sandy loams  of pH  5.5  and 7.0 were  used for the trials. The soils were  contaminated  with  zinc according  to  the following  design:  control (natural  content),  raised  content  (70  mg  Zn2+ kg-1), weakly   polluted  (200 mg  Zn2+  kg-1  ),  moderately  polluted  (500  mg Zn2+  kg-1), heavily  polluted (1,500  mg Zn2+ kg-1)  and very  heavily polluted  soil (5,000  mg and 10,000 mg Zn2+  kg-1).   The  soil  samples  prepared  as  above were  brought  to  the moisture   content  of 50% maximum water  capacity  and incubated  at  25oC for 120 days.  On day  30,  60 and  120, the  activity of dehydrogenases,  ß-glucosidase,  urease,   acid  phosphatase  and arylsulphatase was determined.   Based  on  these  determinations,  the  following  indices  were calculated: ED50, the  index  for resistance  (RS)  and  the  index  for resilience  (RL). The  tests  have  demonstrated  that  as  the  rate  of soil  contamination  with   zinc  increased,  the  activity  of all  the  analyzed   enzymes  was significantly depressed.  The  negative influence   of zinc  contamination   on the  activity of particular enzymes,  irrespective  of the soil  pH,  persisted throughout  the  whole experiment. In  respect  of their  sensitivity to zinc, the enzymes  can  be ordered as follows:  arylsulphatase > dehydrogenases  > acid  phosphatase  > urease  > ß-glucosidase. Zinc contamination caused lasting changes in the  soil environment, but  the  return   to the  state  of equilibrium was  the  quickest  in the case  of dehydrogenases  (RL = 0.276),  less  rapid  for  arylsulphatase  (RL = 0.173)  and the  slowest  for acid phosphatase  (RL = 0.064).  In  contrast,   the activity of urease,  instead of regenerating, was  increasingly disturbed  (RL = 0.350).  Soil acidification was the  factor  that  most evidently  exacerbated  the negative influence of zinc on the activity of ß-glucosidase and arylsulphatase. Values  of ED50  for the activity of particular enzymes  were  varied.   In  the  soil  of pH 7.0, they ranged from 3,324 mg Zn2+ kg-1  for ß-glucosidase to 412 mg Zn2+ kg-1  for dehydrogenases, and  in  the soil of pH  5.5, they varied from 1,008  Zn2+  kg-1   for  ß-glucosidase to 280 mg Zn2+  kg-1  for arylsulphatase.