The aim of this study was to determine the first effect of lead on microbial activity in soil. The study was carried out in the soil samples from four different radish (Raphanus sativus L. var. radicula, Brassicaceae) fields along the highway in a district (Kadirli, Osmaniye) of the Eastern Mediterranean Region, Turkey. After the calculation of Pb contents, the Pb amounts of the soil samples were brought up to 50 and 100 mg Pb kg(-1) by treatment with Pb(NO3)(2), and the samples for the carbon and the nitrogen mineralization were incubated under controlled conditions (28degreesC, constant moist). The carbon mineralization was determined by a CO2 respiration method for 30 days. The nitrogen mineralization was observed in vitro for 6 weeks. The untreated group was statistically different from the 50 and 100 mg Pb kg(-1) treatments in the aspect of the C(CO2) outlet during mineralization (P less than or equal to 0.05), but difference between the 50 and 100 mg Pb kg(-1) treatments was not significant. NH4-N and NO3-N contents of each soil were shown differences between across treatments. Based on these results, it is possible to conclude that the addition of 50 and 100 mg Pb kg(-1) provided a toxic effect threshold for the microbial activity into 30 days.