A drying model was developed for a composite material using the finite-difference method and applied to drying of twigs of "yerba mate". Drying experiments were carried out in a convective dryer with twigs with and without bark for three different diameters: 2.5 x 10(-3), 5.0 x 10(-3) and 7.5 x 10(-3) m. Air temperature varied between 70 and 130 degreesC. Moisture diffusion coefficient value was used to fit the developed model. This parameter was found to be dependent on temperature, moisture content and twig diameter. Moisture diffusion coefficients for xylem were greater than those found for bark. Their values varied between 1.7 x 10(-10) and 8.3 x 10(-9) m(2)/s for xylem and 8.7 x 10(-12) and 4.7 x 10(-9) m(2)/s for bark. Minor values of mean percent error were obtained dividing experiences in two groups: below and above 100 degreesC. (C) 2004 Elsevier Ltd. All rights reserved.