Primary objective: Microencapsulation is a novel method for in vivo immunoprotection of genetically engineered mammalian cells. This study aimed at optimizing alginate/poly-L-lysine/alginate (APA) microencapsulation of mammalian cells in small size (<300 μm) hollow core microcapsules and at evaluating some of the physical characteristics of APA microcapsules produced by different devices and with different alginate preparations. Methods and procedures: Alginate preparations with higher or lower viscosity were used with three different methods: (i) vibrating nozzle, (ii) coaxial gas flow extrusion (AirJet) and (iii) laminar jet break-up (JetCutter). Parameters and device settings for the production of microcapsules with specific characteristics were defined for all three methods. Mechanical stability of APA microcapsules and cell viability of encapsulated cells were investigated in long-term culture and in an animal model. Main results: Uniform spherical beads with a mean diameter <300 mum could be produced by all three encapsulation methods. For the production of uniform microcapsules with a small diameter (<300 μm) the vibrating nozzle technique required a relatively low viscosity of alginate (<0.2 Pa/s), while the AirJet and JetCutter devices performed equally well with alginate of higher viscosity. In all cases, alginate with a lower molar mass was inferior to higher molar mass alginate in terms of mechanical stability of the microcapsules. Microcapsules with optimized mechanical properties were injected intravascularly in rats and shown to maintain their shape and the viability of encapsulated cells. Conclusions: The described methods and devices are able to produce APA microcapsules of small size and uniform shape which are mechanically stable in culture and may maintain the viability of the enclosed cells over extended periods of time. These microcapsules seem to be suitable for further therapeutic studies in an animal model of human disease.