This report deals with stability and toxicity of urea-formaldehyde (UF) adhesives for woodworking industry. ATR FTIR method was used to research UF adhesive modified by glutaraldehyde (GA). The glutaraldehyde was added to UF resin to increase structural stability of the adhesive. FTIR spectra of UF adhesives, UF and GA blends hardened at temperature 100 °C are presented in the paper. Formaldehyde released from the adhesive is harmful. Collagen solution was chosen as reaction agent to decrease UF adhesive toxicity. Measured FTIR spectra of UF adhesive modified with collagen hydrolysate approved the creation of bonds between formaldehyde and collagen.