To evaluate one the effects of interferon (IFN) and its inducers on neutrophil functions neutrophil chemiluminescence (ChL) was assayed on 31 healthy individuals, nine patients treated with IFN-α (human lymphoblastoid interferon, 3×10(6)units/day i. m. daily) and 11 patients treated with Ge-132 (2,250mg/day p. o. daily). The base lines (BLs), peak levels (PLs) and times to PLs (PLs) of neutrophil ChL were examined before, one week and one month after the treatment. The direct effects of IFN-α, Ge-132 and OK-432 on neutrophil ChL were also evaluated by using an in vitro experimental system. PLs were significantly increased one week after the treatment with IFN-α or Ge-132. However, they were decreased to the pretreatment level one month after the treatment. In vitro experimental system IFN-α enhanced PLs of neutrophil ChL showing dose and time dependencies. On the other hand Ge-132 and OK-432 showed no direct effect on neutrophil ChL in vitro. These findings suggest that IFN-α and Ge-132 enhance the host defense mechanism by the activation of neutrophil functions, and also suggest that they have some benefits not only in the clinical management of cancer but also of chronic infection.