Between June 1988 and October 1989 the effect of soil compaction on abundance and biomass of active lumbricids was investigated in a longterm field experiment under spring-wheat and winter-barley. Seven plots were subjected to loads by agricultural machinery under conditions simulating three common kinds of agricultural practice and compared to an unloaded control plot (Table 1). The dominant species of the investigation area, Aporrectodea caliginosa and A. rosea (99.3% of total individual number) had their highest activity and biomass in the uncompact control plot. Lowest individual numbers were found in the extremely loaded wheel-track and the conservation tillage area. The extensive cultivation of this area began just at the start of the field experiment, so that a greater earthworm population had not had time to establish itself. In pot experiments the activity of the endogeic species A. caliginosa was investigated in tripartioned soil columns (40 cm long × 19 cm wide), each differently compact to pore volumes (pv) of 37.5, 42.5, 47.5 and 56%. A significantly higher activity, measured as the length and the number of the burrows visible from outside, was found in the lighter substrates. The volume number extent of earthworm burrows was as much as 2 times higher in the 47.5 and 56% pv columns than in the more compact 42.5 and 37.5% pv columns.