Cyanine-based near-i.r. fluorescent probes have been applied as labels to determine functional groups in polymeric materials. The advantage of such probes is that they can be applied to polymers which are autofluorescent or strongly coloured or to strongly scattering polymer emulsions. Two examples are discussed : the labelling of a polymer latex with aldehyde functional groups, by application of a cyanine with a hydrazide functionality, and the labelling of amino functional groups in a polyamide utilizing a cyanine label with an isothiocyanate functionality. The cyanines which have been applied absorb and fluoresce in the 650-700 nm range and in the 750-800 nm range, respectively. In addition to near-i.r. fluorescence, the cyanine dyes have strong absorption (with extinction coefficients in the order of 2 x 10(5) l mol(-1)cm(-1)). It is shown that by application of reflection absorption measurements also sensitive detection of labelled functional groups can be realized. The combined application of fluorescence and reflection measurements allows for the detection of concentration and distribution of functional groups in polymeric systems down to very low levels.