G-actin was prepared from pork liver by gelfiltration on AcA 44 Ultrogel. The purity of the actin was 95-98% and the yield was 45-150 mg from 500 g liver, corresponding to a maximum efficiency of recovery of about 30%. High viscosities of actin-enriched solutions were reduced by a specific pH-step. In SDS-gel electrophoresis a single band of about ~ 45000 daltons was seen. The G-actin was polymerizable as shown by high shear viscosity measurements. The isoelectric points of the β- and γ-isoactins were 5.6 and 5.7.