Properties of calcium carbonate precipitated from aqueous solutions of CaCl2 and Na2CO3 in the presence of sodium dodecyl sulfate (SDS) and S-S 0.1 T magnetic field (MF) were studied. The nucleation and precipitation processes of CaCO3 were investigated by PH and zeta potential measurements at 20 +/- 1 degrees C up to 2 h after mixing the solutions. Also the amounts of calcium carbonate deposited on the glass surfaces and its structure were examined. It was found that SDS influences the kinetics of precipitation, crystallographic forms, and crystal size of CaCO3. The SDS effects are more pronounced in MF presence. A small amount of SDS accelerates transformation of vaterite into calcite, whereas increasing surfactant concentration moderates such a transformation. On the other hand, in all the systems, MF in the presence of SDS causes a slower transformation of vaterite into calcite. These effects are reflected in PH and potential changes, although there is no clear dependence between the SDS amount present during the precipitation and changes of the parameters investigated. It seems that MF effect is most significant at a defined optimal SDS concentration. The results, however, do not allow suggestiion of any detailed mechanism of the field interaction.