A new mechanism of cell damage by alternating magnetic field with hematoporphyrin is described. C6 glioblastoma cell suspensions were exposed to an alternating magnetic field with frequency 180 kHz up to 60 min in the presence of hematoporphyrin in H2O and in D2O. The results presented suggest that an alternating magnetic field is able to activate hematoporphyrin, and this method may be a basis for cancer treatment.