A method to identify different tissues in ultrasound images is presented. Assuming a Rayleigh modelfor speckle, the different tissues present in the image will be related to the Rayleigh a parameter; with different values for each different tissue. The parameter is locally estimated using well known estimation methods for the Rayleigh distribution, such as the Maximum Likelihood estimator A significant increase in the separability of the different tissues present in the image is then achieved. A subsequent clustering process based on the position of the maxima of the estimator distribution allows the classification ofeachpixel in a tissue class.