Specific particle charges, defined as the particle charge-to-mass ratio or the net charge per unit mass, in fluidized beds have been deduced from signals registered by a miniature ball probe when a single gas bubble passed the probe in a fluidized bed based on a recently developed charge induction and transfer model. The results indicate that the specific charge is insensitive to the size of single bubbles passing the probe. The increase of relative humidity at RH < 40% resulted in a significant decrease of specific charges, and the effect of relative humidity became insignificant beyond 40% relative humidity. The results are of similar magnitude to specific charges reported in the literature from direct measurements using Faraday pails. (C) 2003 Elsevier B.V. All rights reserved.