In polyoxin-resistant strains of Alternaria kikuchiana, the synthesis of cell-wall chitin was scarcely inhibited by polyoxin B, although chitin synthetase preparations of them showed a level of polyoxin sensitivity similar to those of sensitive strains. A decrease of14C-labelled polyoxin uptake was correlated with an increased level of polyoxin resistance in various strains. The amount of14C-polyoxin A or3H-polyoxin A accumulated in a highly resistant strain was less than 10% of that in a sensitive strain. These results indicate that resistant strains have a reduced capacity to take up polyoxin A or B.