The sensitometric effects of pre-exposure heating in TDPM of the Dry Silver type were investigated. Loss of developable density with increasing time of pre-exposure heating was shown to involve the toners which are essential to selective, image-wise TDPM development. Pre-exposure heating was found not to affect the latent image forming system (silver halide-silver carboxylate interface) in TDPM. Our observations support previously proposed interpretations of the mechanism of TDPM development. Preexposure heating may thus lead to either (a) loss of toner, e.g., by volatilization or air oxidation, and/or (b) side reactions between toner and silver carboxylate leading to formation of less reactive species. From a practical point of view these results provide mechanisms for both the storage instability of the TDPM sensitometric responses, as well as for inefficiency in latent image amplification.