In model experiments with equimolar mixtures of lysinemonohydrochloride and glucose [88% (w/v) water content, 100 degrees C heating temperature] the influence of several conditions (hydrolysis, pH) and ingredients (iron, phosphate, and nitrite) on the formation of N epsilon-carboxymethyllysine (CML) were evaluated. CML was analysed using a reversed-phase HPLC-method after derivatisation with o-phthaldialdehyde. CML, which is an oxidative derivative of fructoselysine, is also formed during the acid hydrolysis applied for amino acid determination in food products. In model mixtures without hydrolysis only 8-21% CML compared to that in hydrolysed samples was found. Therefore, in food products all hydrolyses for CML must be performed after borohydride reduction in order to destroy fructoselysine. This can be controlled by the determination of furosine. The pH of the model mixtures considerably influenced the formation of CML. At pH 4.0 only 70 mg, at pH 7.0 370 mg, and at pH 9.0 3170 mg CML/kg lysine were determined. The CML concentration also clearly increased with higher concentrations of iron, phosphate, and nitrite. This is explained by a promoting effect on the oxidation of fructoselysine to CML.