Respiration and nitrogen immobilization of the fresh organic layer of an acid podzol were studied, after pretreatment with sulfur, to simulate sulfur treatment of microsites when sulfur-coated urea is applied to the soil. The laboratory incubations were done at 10 and 20°C with several levels of urea application. Urea hydrolysis was slowed down considerably at 10°C in materials that had been pretreated with sulfur. Sulfur pretreatment modified the increase in pH and respiration caused by urea application but had little influence on the availability of ammonium nitrogen. The lower temperature allowed adequate fertilizer nitrogen recovery from moderate dosage rates that produced a pH lower than neutrality. At the higher temperature, fertilizer nitrogen recoveries were very poor. At higher pH, a large part of the immobilization of nitrogen appears to be nonmicrobial.