Tagging experiments have been used to study the migratory behaviour of the spiny lobster Panulirus argus (Latreille), off Ceará State, Brazil. An analysis based on vectorial theory has provided the calculation of the coefficient of directional dispersion ( V), the coefficient of randon disperson (a² ) and the centre of density, by quarters of the year. The lobsters were found to engage in breeding migration in the second quarter, when there is a low random dispersion and in feeding migration in the third and fourth quarters, when there is high randon dispersion. The spawning areas are located in offshore regions and the lobsters reach them by moving seawardly, from positions occupied nearer the cost, in the fourth quarter.