The loss of genetic information from a number of specific regions of the genome has been documented in human tumors in vivo. To estimate the frequency with which IFN beta 1 gene loss occurs in human gliomas, both restriction fragment length polymorphism (RFLP) analysis and polymerase chain reaction (PCR) amplification, using the IFN-gamma gene as a reference, were used and the results obtained with the two methods were compared. The relative intensity of PCR bands (IFN beta 1/IFN gamma) in the gliomas with loss of heterozygosity for the IFN beta 1 was significantly different (P < 0.05) with regard to the gliomas with the IFN beta 1 gene. Consequently, these findings indicate that differential PCR is a reliable and non-radioactive method of demonstrating gene loss in tumors.