Lateral dispersion was investigated in water unsaturated columns (length 18 or 20 cm and diameter 6 or 11 cm, respectively) at constant flow (q = 28.5 mm h - 1 ). Columns were either packed homogeneously with fine sand and coarse sand, or in horizontal or inclinded layers. A conservative dye tracer was applied as a point source in the centre of the column or as a pulse over the entire surface. Lateral mixing of the point source was investigated visually by cutting the columns vertically into two halves immediately after the dye was detected in the outflow. In non-stratified, homogeneously packed columns lateral solute mixing could be modelled using a convection-dispersion model with lateral dispersion term. In stratified columns, processes at or just above the layer boundaries significantly modified lateral mixing. These processes depend strongly on the sequence of neighbouring layers. In a fine textured layer overlying coarse sand streamlines may converge and thereby induce preferential flow. In a coarse layer immediately above a fine textured one lateral exchange of flowing solutes may be enhanced and thereby smooth out a moving solute front.