Investment strategies in multiplicative Markovian market models
with transaction costs are defined using growth optimal criteria.
The optimal strategy is shown to consist in holding the amount of
capital invested in stocks within an interval around an ideal
optimal investment. The size of the holding interval is determined by the intensity of the transaction costs and the time horizon. The inclusion of financial derivatives in the models is also considered. All the results presented in this contributions were previously derived in collaboration with E. Aurell.