To further validate its use in positron emission tomography (PET), we studied the binding of [18F]altanserin, a specific 5HT2 radioligand, in the rat brain using in vivo autoradiography. Distribution of [18F]altanserin binding was comparable to the in vitro mapping of 5HT2 receptors reported in the literature. Selective displacers were used to test the reversibility and the selectivity of this radioligand. Specific binding of [18F]altanserin in the rat frontal cortex was quantified by direct counting with an electronic imaging system and by quantification on digitalized autoradiograms. Close results of about 30 pmol/g were obtained with both methods. Our data confirmed that [18F]altanserin is a valid tracer for 5HT2 receptors binding studies.