Studies were conducted on Nicotiana tabacum 1507 cultivation in an aqueous two-phase system (PD(5)) formed by adding 4% PEG (MW 20,000) and 7.5% dextran (MW 70,000) to the medium. The time course of growth and changes in the phase volumes of the PD(5) system, as well as the biosynthesis, secretion, and partitioning of phosphomonoesterases during 11 days of cultivation, were followed. In comparison with N. tabacum 1507 cultivation as a free suspension, on day 8 of cultivation in the PD(5) system the yields of acid and alkaline extracellular phosphomonoesterases were 18 and 10 times higher, respectively. Partitioning took place mainly in the bottom phase with specific activity being 4.5 and 3.5 times higher, respectively. (c) 1996 John Wiley & Sons, Inc.