In this work we propose a method to characterize multi-pixel Geiger-mode (MPGM) avalanche photodiodes (APDs) and present systematic studies of new devices from three different manufacturers. The basic properties of MGPM APDs such as gain, photon detection efficiency, excess noise factor and noise, as well as their dependence on operating voltage have been measured. Spectral response was measured in the range 350-800nm. It was shown that despite very good pixel-to-pixel gain uniformity, the excess noise factor of these APDs can be significantly greater than 1. (c) 2006 Elsevier B.V. All rights reserved.