The present invention relates to magnetic beads suitable for, for example, isolation of proteins, cells, and viruses and also for diagnostic applications and cell cultivation. The magnetic beads are composite beads with an inner core of metal particles, which are coated with an inert synthetic polymer and these are then enclosed in a hydrophilic porous polymer, preferably agarose. This provides porous biocompatible beads without metal leakage. The beads may be used for cell cultivation or for chromatography. When the beads are used for chromatography the agarose layer is preferably provided with ligands having affinity for selected biomolecules.