The effects of two calcium compounds on N transformation in tropical Hawaiian soils were investigated. The C02 production in the Akaka soil was enhanced by lime and depressed by calcium chloride, as compared with the control, and the rate of production was not affected by the addition of NH4-N. The results of this investigation suggest that the Ca2+ ion in lime play a similar role in N mineralization to those in calcium chloride. This may be regarded as contributory to the much-emphasized influence of lime on microbial stimulation in causing N mineralization. The immobilization of added N was greater in Ca(OH)2-treated sample than in those receiving CaCI2.2H20. The former accelerated but the latter curtailed nitrification.