Abstract Depth dose distributions in a water phantom and total tissue dose rates were measured for neutron beams from a 30-inch isochronous cyclotron producing 8 MeV deuterons, 15 MeV protons, or 23.2 MeV helium-3 ions using various targets. The reactions employed were 9Be(3He,n), 9Be(p,n), 9Be(d,n), 2H(p,np), and 7Li(d,n). The influence of target construction on beam characteristics was examined. At various phantom depths, gamma-ray contamination and fast and thermal neutron fluxes were measured. The authors conclude that a small medical cyclotron is a satisfactory source of fast neutrons for radiobiological and dosimetric research and has possible clinical study applications.