Separation of proteins and dipeptides by plain spiral tube and cross-pressed tube assemblies. Apparatus: type-J coil planet centrifuge with 10 cm revolution radius; separation column: plain spiral tube assembly: 9 spiral layers of ca 40 m long, 1.6 mm I.D. FEP tube with a total capacity of 103 ml; cross-pressed spiral tube assembly: 9 spiral layers of ca 40 m long, 1.6 mm I.D. FEP tubing cross-pressed at 1 cm interval with 95 ml capacity; Protein separation: Solvent system: 12.5% (w/w)PEG1000-1.25%(w/w) potassium phosphate in water: for dipeptide separation: sample: lysozyme and myoglobin, each 5 mg in 1 ml of upper phase; elution mode: L-I-T, flow rate: 1 ml/min; detection: 280 nm. revolution: 800 rpm. Dipeptide separation: elution mode: L-I-T, flow rate 2 ml/min; other conditions are described in Fig. 3. SF: solvent front.