The isolation and characterization of cDNAs encoding poly(ADP-ribose) glycohydrolase (PARG) enzymes and the amino acid sequences of PARGs from several species are described. PARG is involved in the cellular response to DNA damage and its proper function is associated with the body's response to neoplastic disorder inducing agents and oxidative stress. Expression vectors containing the cDNAs and cells transformed with the vectors are described. Probes and primers that hybridize with the cDNAs are described. Expression of the cDNA in E. coli results in an enzymatically active protein of about 111 kDa and an active fragment of about 59 kDa. Methods for inhibiting PARG expression or overexpressing PARG in a subject for therapeutic benefit are described. Exemplary of PARG inhibitors are anti-sense oligonucleotides. The invention has implications for treatment of neoplastic disorder, heart attack, stroke, and neurodegenerative diseases. Methods for detecting a mutant PARG allele are also described. Antibodies immunoreactive with PARGs and fragments thereof are described.