A polyclonal antibody against glucomannans (GMs) was raised in a mouse. A dot-blot immunoassay and competitive-inhibition tests indicated that the antibody was specific for GMs. The antibody enables visualization of the localization of GMs in differentiating tracheids of Chamaecyparis obtusa. Labeling of GMs was restricted to the secondary walls of the tracheids. The labeling density temporarily increased and then decreased in the outer and middle layers of the secondary wall during cell wall formation. This ii probably due to the accumulation of lignin. In comparison with previous studies of glucuronoxylans, there must be a clear difference between the deposition of GMs and that of glucuronoxylans.