A parainfluenza multiplex nucleic acid assay is a multiplex in vitro diagnostic test for the simultaneous qualitative detection and discrimination of parainfluenza 1 virus, parainfluenza 2 virus, parainfluenza 3 virus and parainfluenza 4 virus nucleic acids isolated and purified from human respiratory specimens obtained from individuals exhibiting signs and symptoms of respiratory tract infections or viral culture. The detection and discrimination of human parainfluenza nucleic acids from symptomatic patients aid in the diagnosis of human respiratory tract parainfluenza infections if used in conjunction with other clinical and laboratory findings.