NOVELTY - The scaleable bioreactor comprises a cassette comprising a manifold and an arrangement of hollow fiber membranes, and upper and lower headplates (1), where the cassettes (5) are modular components adapted to cooperate with each other and the headplates to define an internal extra capillary culture space (3). Each arrangement of hollow fiber membranes comprise a discrete inlet and outlet reservoir located at a manifold at each end of the membranes. Each reservoir is in fluid communication with the respective inlet or outlet. The hollow fiber membranes are arranged in a layer.    USE - The scalable capillary membrane bioreactor is useful for culturing and maintaining cells such as mammalian and insect cells and/or microorganisms such as bacteria including Bacillus subtilis, Escherichia coli and Staphylococcus, yeasts and fungi for exploiting the metabolism of the cells for the production of biological products or biotransformations, and useful in wastewater treatment, where the cells include anchorage dependent cell lines selected from normal diploid cell strains e.g. human embroyonic lung and human foreskin, primary cells such as monkey and dog cells, established and transformed cell lines e.g. mouse fibroblasts and normal rat kidney.    ADVANTAGE - The scalable capillary membrane bioreactor is capable of economically, energy efficiently culturing and maintaining cells and/or microorganisms with increased flexibility thus effectively exploiting the metabolism of these cells for the production of biological products/biotransformation, and facilitates consistent fluid delivery throughout the cell culturing space thus resulting in improved metabolism and cell viability.    DETAILED DESCRIPTION - The scaleable bioreactor comprises a cassette comprising a manifold and an arrangement of hollow fiber membranes, and upper and lower headplates (1), where the cassettes (5) are modular components adapted to cooperate with each other and the headplates to define an internal extra capillary culture space (3). Each arrangement of hollow fiber membranes comprise a discrete inlet and outlet reservoir located at a manifold at each end of the membranes. Each reservoir is in fluid communication with the respective inlet or outlet. The hollow fiber membranes are arranged in a layer of parallel membranes. Each cassette includes a hollow fiber membrane layer (row) per functionality, where the hollow fiber membrane layer is arranged perpendicular to the layer above and/or below it within either horizontal orientation or vertical orientation. Each row of hollow fiber membrane is offset against the row of membranes above and/or below it. INDEPENDENT CLAIMS are included for:    (1) a cassette;    (2) a kit for a bioreactor; and    (3) a process for exploiting the metabolism of cells and/or microorganisms.    DESCRIPTION OF DRAWING(S) - The diagram shows a perspective view of a scalable bioreactor.    Headplates (1)    Panel (2)    Extra capillary space (3)    Cassette (5)    Pin. (6)