A guard for a power transmission shaft such as a tractor pto shaft 18,20 comprises a flexible convoluted tubing 24 with end couplings 26 which together totally enclose the rotating parts. The tubing 24 can extend and retract axially to suit a variety of shaft lengths, and can flex transversely to accommodate turning of the tractor/implement combination. A tube 34 journalled on bearings 36, or equivalent bearing means, prevents damage to the tubing 24 by the shaft 18,20.