The precipitation of barium sulfate was investigated by photon correlation spectroscopic (PCS) measurements of the growing crystals combined with electrical conductivity measurements of the mother solution. Small silica seeds (36 nm) were added to the solution. Therefore, heterogeneous nucleation did not take place on the walls and on the stirrer, which is usually the case, but on the seeds. Hence the growth of the crystals which had nucleated on the seeds could be studied by PCS. In order to avoid the ill-conditioned inversion of the measured raw data, the autocorrelation functions, a population balance model was used to calculate these functions with the help of a kinetic model taken from the literature. The measured and the calculated autocorrelation functions should coincide and adjustable parameters were found from a least-squares fit. The measurements revealed that nucleation is strongly enhanced by PMA-PVS (polymaleic acid-polyvinylsulfonic acid). However, a simple model which assumes Langmuir adsorption of PMA-PVS on the crystal surface did not describe the kinetics very well. The nucleation rate in the absence of the additive was found to be J=1.3 . 10(10) exp(-27/ln(2)S) [m(-3)s(-1)], while the growth rate was G=2.6 . 10(-8)(S-1)S-2/3(1/3) exp(-29/3 ln S) [m s(-1)]. These results match results taken from the literature fairly well.