Treatment of TMP Beech- and Spruce fibres with the enzyme laccase (EC 1.10.3.2) in an aqueous suspension is known to modify fibre surface properties. Although some experimental techniques show effects of the treatment, the fundamental nature of the modification is not known: This work is an attempt towards a clarification of this issue. The luminescence measurements indicate that the modification in a pronounced way involves the electronic state of the lignin in contrast to apparently missing effects on eg. the vibrational modes of the lignin.