In human T lymphocytes immunoblotting analysis of phosphoinositidase C (PIC) isoforms has shown that gamma 1 is the most represented isoform both at the cytoplasmic and nuclear level, and that interferon beta produces, within 90 min of treatment, an increase of its expression. These results, also supported by immunoelectronmicroscopic investigation, strongly suggest the involvement of PIC gamma 1 in the cascade of molecular events generated by the interaction between interferon and its cell surface receptors.