The effects of wastewater sludge amendments on nitrogen forms and urease activity in soil and earthworm (Lumbricus terrestris) casts were investigated. Two different wastewater sludges (municipal and canned food industry) were added to clay loam agricultural soil samples at doses of 20, 40 and 80 g dry raw sludge kg(-1). Following sludge amendment, an incubation study was performed and mineral nitrogen (NH(4)(+)-N+NO(3)(-)-N), total-N and urease activity were determined in soil and earthworm casts. Results indicated that the addition of wastewater sludge significantly increased urease activity, mineral-N and total-N contents of soil and casts. Furthermore, urease activity, mineral-N and total-N contents of casts were found to be significantly higher than that of the surrounding soil. Application of canned food industry sludge at a dose of 80 g kg(-1)(200 t ha(-1)) was the most effective application on nitrogen and urease contents. On the other hand, 40 g kg(-1) (100 t ha(-1)) treatment was found to be the most suitable dose for municipal wastewater sludge.