A computer-aided comparison of tomato (Lycopersicon esculentum Mill.) seed protein patterns, obtained after two-dimensional gel electrophoresis, was made for three different extraction procedures: TCA acetone/lysis buffer, lysis buffer only and modified Laemmli/lysis buffer. Comparison of the isolation methods showed that about half of the amount of proteins detected was common in each method. Also, proteins specific to some isolation methods were detected. Protein synthesis during imbibition was monitored using 35S-methionine. After labelling the proteins were extracted using TCA acetone/lysis buffer. Following two-dimensional gel electrophoresis the gels were first silver stained, to give a general picture of all proteins present in the seed, then the gels were exposed to a film for autoradiography. Comparison of the in vivo-synthesized protein patterns and the silver-stained proteins revealed that from day 0 to day 1 the protein pattern was changed but the total number of different spots was similar. After 1 day of imbibition, the number of protein spots increased greatly and the protein pattern changed again.