We have studied the photosensitizing effects of zinc(II)-phthalocyanine (ZnPc) on the cytoskeleton of HeLa cells using sublethal (10(-7) M, followed by 1 or 3 min of red light to induce 20%, LD20, or 60%, LD60, cell death, respectively) or lethal (5 x 10(-6) M and 15 min of irradiation, LD100) experimental conditions. The immunofluorescent analysis of the cytoskeleton showed a variable photodamage to microtubules (MT), actin microfilaments (AF) and intermediate filaments of keratin (KF), as well as on alpha-actinin, which was dependent on treatment conditions. Both sublethal treatments induced deep alterations on interphase and mitotic MT. The mitotic index increased with time with the maximum at 18 h (12%) or 24 h (14%) after LD20 or LD60, respectively. The alterations on AF and alpha-actinin were much more severe than those observed on KF at any evaluated time. With the exception of the KF, which remained partially organized, the MT and AF network was severely damaged by the lethal treatment. Western blot analysis for alpha-tubulin, G-actin and alpha-actinin from soluble and insoluble fractions confirmed the results observed by immunofluorescence, thus indicating that these cytoskeletal components are involved in cell damage and death by ZnPc photosensitization.