Abstract The current standard way of using biocide in coatings for protection against micro-organic surface growth, so called biofouling, is insufficient as the biocide leaks out from the coating too fast. In this article, we investigate a method for prolongation of the coating protection by slowing down the release rate of biocides in a controlled way. The biocide is placed into micrometer-sized reservoirs, called microspheres, from where it is slowly distributed into the coating. By different microscopic techniques the microspheres were found to be compatible (i.e. no phase separation was observed) both with the coating material and the paint. Biocide release from the coating is recorded by liquid scintillation counting and it was clear that the release is considerably slower from coatings with microspheres compared to an ordinary formulation with freely dispersed biocides. Microspheres might thus be a beneficial tool for the development of coatings with a longer protection against biofouling.