The purpose of the observations was the viability and quality evaluation of E. coli bacteria encapsulated in hollow fiber membranes (HF) in short in vivo and in vitro experiments. A polypropylene, surface-modified hollow fiber was applied for immunoisolation of E. coli bacteria transfected with a green fluorescent protein (E. coli GFPI). The presence of GFP fluorescence of organisms was assessed with the use of flow cytometry. The E. coli GFPIs were then observed for the period of 5 days in in vitro experiments in the culture medium. A single IPTG (isopropyl beta-D-1-thiogalactopyranoside) induction of GFP gene appeared to be adequate for an expression of GFP protein for 5 days. The GFP expression values observed for E. coli GFPs encapsulated in HF during culture in different culture media were comparable. The survival of E. coli GFPIs encapsulated in HF after 1, 2, 4, or 5 days of subcutaneous implantation into mice was evaluated. The explanted E. coli GFPIs exhibited mean expression 603 +/- 17 (n = 32) units of fluorescence during the implantation period. The values obtained were comparable for selected days of observation. It was observed that the membranes applied ensured the bacteria growth within the HF's space only.