An enzyme-linked immunosorbent assay (ELISA) was used to detect and quantify Postia placenta (Fr.) M. Lars. et Lomb. in decaying wood. The fungus was detected as early as ten days after inoculation suggesting that ELISA may be effective in detecting early incipient decay. Decay-induced weight loss in P. placenta decayed spruce blocks was correlated with the absorbance values obtained in the ELISA reaction.