In this paper we analyze the effects of the time modulation of (zeroth-order) Bessel beams, by considering a few different pulse shapes. Namely, three modulating functions are considered: a train of rectangular waves, a single rectangular pulse, and a gaussian pulse. The influence of the carrier frequency, and of shape and spectral bandwidth of the modulating function, is also discussed; while further support to our results is met by using the convolution technique in the time domain. At the beginning, a brief review of the X-shaped solutions to the wave equation, and of some properties of theirs, is presented. (C) 2003 Elsevier B.V. All rights reserved.2294179199107