Feline neutrophils (PMN) were isolated and exposed to ultraviolet light-inactivated feline leukaemia virus (UV-FeLV) and purified envelope component p15E (FeLV-p15E). Functional capacity of exposed PMN was measured in vitro utilizing the chemiluminescence (CL) response. PMN exposed to UV-FeLV demonstrated depressed CL responses to Ca2+-ionophore A23187 and latex particles. However, FeLV-p15E produced significant suppression in the CL response to A23187 but failed to produce significant alterations in response to latex particles. The data indicate that FeLV-p15E may, in part, be responsible for increased morbidity and mortality among FeLV-infected cats through suppression of the PMN population.