The occurrence of +Gz-induced loss of consciousness (G-LOC) is well recognized in high-performance aircraft. A case of G-LOC is described involving a co-pilot on a flying instructor's course in a propeller-driven aircraft, the CT-4. The cause of G-LOC is attributed to a combination of a lack of recent G exposure, not commanding the aircraft, fatigue, and a possibly less-than-optimal straining manoeuvre. This case reinforces the problems of G-LOC in any aircraft capable of performing aerobatics.