HYPERICIN, A POLYCYCLIC aromatic dione isolated from plants, is presently being clinically evaluated as an antiviral agent in the treatment of human immunodeficiency virus (HIV) infection. In addition, it is known to be a potent protein kinase C inhibitor. To evaluate its potential as an inhibitor of glioma growth, an established (U87) and low-passage glioma line 93–492 were treated with hypericin in tissue culture for a period of 48 hours after passage. Hypericin inhibited the glioma growth in a dose-related manner, with a marked inhibition of growth in the low-micromolar concentration range (e.g., in line U87 and low-passage line 93–492, a concentration of hypericin of 10 μmol/L produced 62 and 76% decreases in [3H]thymidine uptake, respectively). Because the reported inhibitory effects of protein kinase C are enhanced by visible light, [3H]thymidine uptake was measured in both the presence and the absence of visible light. In glioma line A172, the presence of light slightly increased the inhibitory effect of hypericin. Moreover, an apoptosis (i.e., programmed cell death) assay was performed to determine whether the treatment of glioma cells with hypericin was cytostatic or cytocidal. Cells were harvested, and purified deoxyribonucleic acid (DNA) was analyzed by agarose gel electrophoresis. DNA from cells treated with hypericin for 48 hours exhibited a classical “ladder” pattern of oligonucleosome-sized fragments characteristic of apoptosis. These data suggest that the proven safe drug hypericin may have potential as an antiglioma agent; we suggest clinical trials.