A technique for measuring the fast 3He++ distribution during 3He++ minority ion cyclotron resonance frequency heating is discussed. The technique involves the use of 10- to 100-keV neutral helium beams to neutralize the fast 3He++ ions by double charge-exchange (3He++ + 4He0 → 3He0 + 4He++). The neutralized fast 3He atoms then escape from the plasma and are detected by conventional neutral particle analyzing apparatuses. By the use of such a technique, the effectiveness of the coupling of the ion cyclotron waves to the 3He++ minority can be measured.