In this paper, we consider pooling schemes in which samples are to be tested in two-stages. We show that when batch size is limited as well as pool size, selection schemes tend to be more efficient and flexible. Formulae for the efficiencies of square arrays in all dimensions and for all selection schemes are given in the Appendix. A Fortran program has been written to find whether the most efficient scheme under constraints of batch and pool size be ‘square’ or ‘selection’. Copyright © 2010 John Wiley & Sons, Ltd.