Magnetic field effects on CaCO3 adhesion to substrates were evaluated statistically as for the number of crystals, the occupied surface area per crystal and the crystal size distributions. CaCO3 was precipitated from Na2CO3 and CaCl2 Solutions, which prior to precipitation were or were not exposed to a magnetic field under flowing conditions. Glass, copper and stainless steel plates were used as substrates. The precipitation process occurred at 30degreesC, and in the case of glass plate experiments were also conducted at 60degreesC. The CaCO3 deposits were photographed using an optical polarizing microscope equipped with a camera and then the images were analyzed statistically. For each system studied 14 plates were used. It was found that in all systems the magnetic field (MF) influenced the number of crystals deposited and their size distribution. The changes were statistically significant (t-Student's test). The nature of the substrate surface was found to have a significant effect on the amount of CaCO3 deposited. However, the average amount of calcium carbonate deposited on the glass surface at 30degreesC determined from 14 analyzed plates was only slightly less than that from MF-treated solutions (0.689 and 0.748 mg/cm(2), respectively), and it was practically the same at 60degreesC (0.539 and 0.534 mg/cm(2)). At this higher temperature the deposition of calcium carbonate was reduced relative to that at 30degreesC. From the results obtained it may be concluded that the MF affects both nucleation and crystal growth of CaCO3.