The pharmacology and antiviral effects of various double-stranded polyribonucleotides are being studied. The results of a randomized double-blind study of Poly I:C treatment of varicella-zoster infection in patients with cancer will soon be statistically analyzed and reported. A study of the use of Poly I:C for the prophylaxis of varicella infection in children with cancer after exposure to varicella is now ongoing. Additionally, we have revised our protocols for the above studies in order to evaluate Poly I:C-lysine (Poly I:C-LC) in randomized studies as treatment for varicella-zoster in the prophylaxis of varicella. Poly I:C-LC will also be evaluated as treatment of biopsy-proven viral pneumonia in cancer patients. Finally, we are preparing a batch of another modified Poly I:C (Poly I coupled to a partially thiolated Poly C (Poly I:MPC) which has been shown, in vitro, to avoid the hyporesponsive effects observed with repeated doses of Poly I:C. This polymer will undergo further evaluation as an antiviral agent and the appropriate safety testing to determine the feasibility and its clinical use.