the key parameters of a formulation for measuring particle size the following main methods may be employed sieves sedimentation electrozone sensing coulter counter microscopy low angle laser light scattering lalls the crystalline linezolid form iv of the present invention has a preferred maximum particle size of 500 u03bcm preferably the particle size is less than 300 u03bcm less than 200 u03bcm less than 100 u03bcm or even less than 50 u03bcm another embodiment of the present invention is a pharmaceutical formulation comprising a therapeutically effective amount of crystalline linezolid form iv combined with a pharmaceutically acceptable excipient or carrier another embodiment of the present invention is a method for treating a patient suffering from a gram positive bacterial infection comprising the step of administering to the patient the pharmaceutical formulation comprising a therapeutically effective amount of crystalline linezolid form iv the crystalline linezolid form iv of the present invention used to prepare pharmaceutical formulations may be substantially pure with respect to other crystalline forms i e the pharmaceutical formulations may contain less than about 10 preferably less than about 5 and even more preferably less than about 1 by weight of other crystalline forms of linezolid in particular the pharmaceutical formulations may contain less than about 10 preferably less than about 5 and more preferably less than about 1 and even more preferably less than 0 5 by weight of crystalline linezolid form ii in certain embodiments the pharmaceutical formulations may contain less than about 10 preferably less than about 5 and even more preferably less than about 1 by weight of amorphous linezolid in other embodiments pharmaceutical.