ESR measurements of ion implanted silicon are presented. Silicon wafers implanted with various doses of boron and arsenic ions were investigated. For unannealed samples the defect centre spectrum was established and its dependence on implantation dose was followed. From saturation effects the relation between the relaxation times of various point defects was established. For samples implanted with arsenic ions and annealed ESR signals from arsenic incorporated into the host lattice of the silicon substrate have been found.