Novel pyrazolo[3,4-b]indole nucleoside analogs were synthesized from the corresponding 3-formyl-2-chloroindole and 3-cyano-2-chloroindole nucleosides by treatment with hydrazine. Very few examples of pyrazolo[3,4-b]indole heterocycles have been published in the literature and this is the first synthesis of nucleoside analogs containing this heterocycle. These new pyrazolo[3,4-b]indole nucleosides were active against human cytomegalovirus and herpes simplex virus type 1, but this activity was not well separated from cytotoxicity.