The recombinant green fluorescent protein (gfp(uv)) was expressed by Escherichia coli DH5-alpha cells transformed with the plasmid pGFPuv. The gfp(uv) was selectively permeabilized from the cells in buffer solution (25 MM Tris-HCl, pH 8.0), after freezing (-70degreesC for 15 h), by four freeze (-20degreesC)/thaw cycles interlaid by sonication. The average content of released gfp(uv) (experiment 2) was 7.76, 34.58, 39.38,12.90, and 5.38%, for the initial freezing (-70degreesC) and the first, second, third and fourth freeze/thaw cycles, respectively. Superfusion on freezing was observed between -11degreesC and -14degreesC, after which it reached -20degreesC at 0.83degreesC/min.