The rates of cell attachment of the anchorage-dependent mammalian cell line Vero to the gelatin-based macroporous microcarrier Cultispher-G were determined under various conditions. An optimal rate of attachment (0.98 x 10(-2) min(-1)) occurred by an intermittent stirring regimen of 3 min stirring at 40 rpm per 33 min. This stirring regimen appeared to maximize cell-to-bead attachment and minimized cell aggregation which occurred at a broadly comparable rate. A further increase in the rate of cell-to-bead attachment occurred by preincubation of the microcarriers in serum-supplemented medium prior to cell inoculation in a serum-free medium. However, serum supplementation (>5%) was required for maximal cell growth. The pH of the medium had little effect on cell attachment over a broad range (pH 7.1-8.0). An initial cell/bead inoculum of 30 ensured an even distribution of cells on the available microcarriers with a low proportion of unoccupied beads. The rate of cell attachment to Cultispher-G was an order of magnitude lower than the determined value for the charged dextran microcarrier Cytodex-1, which was measured as 9.05 x 10(-2) min(-1). The optimal conditions for cell attachment were significantly different for the two bead types. Cell attachment to the electrostatic surface of the Cytodex-1 microcarriers was highly dependent on pH and serum supplementation. Cell aggregation during attachment to the Cytodex-1 microcarriers was minimal because of the higher rate of cell-microcarrier attachment. The porous nature of the Cultispher-G microcarriers allowed a maximum cell/bead loading of >1400, which was at least 3 times higher than equivalent loading of the cells on Cytodex-1. The Cuitispher-G matrix also allowed the use of higher agitation rates (up to 100 rpm) in spinner flasks without affecting the cell growth rate or maximum cell density.