This invention relates to novel PEGx-GCSF conjugates, wherein x is the amount of PEG per GCSF and ranges from 4 to 8. The invention also relates to PEG[x]-GCSF populations of individual PEGx-GCSF conjugates, wherein [x] is the average amount of PEG per GCSF of the population and is 4 or greater. The inventive compositions have unexpected therapeutic efficacy, while avoiding or substantially reducing the likelihood of adverse side effects.