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The proteins of mature potato tubers can be used for variety identification. Their pattern after electrophoresis or focusing are genetically determined. Various growth regulators applied during the season had no influence. Molecular weights of the protein subunits are uniform and decrease with age of the tuber, often due to depolymerization. Some subunits are linked by S -S-bridges. A proteid characteristic for immature tubers has been discovered. Part of the diversity in charge distribution is based on different degree of amidation; treatment at pH 10 changes the variety-dependent pattern to a picture similar in all varieties. The latter is also true for proteins from immature tubers. Focusing followed by SDS-incubation (with and without ME) and SDS-gelelectro-phoresis revealed that the main proteins which were different in charge had common MW and may derive from a parent protein. The tuber proteins and especially some of the peroxidases are quite resistant to SDS-attack. Only prolonged incubation (50 °C, 40 hours) with SDS brings about digestibility. A borate buffer, pH 7.9 has been used, making possible the electrophoresis of undiluted, unfractionated sap or other crude mixtures of proteins. Some new versions of two-dimensional techniques with PAA as a carrier are applied in order to differentiate between charge, shift of charge, and MW

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