This paper explores the influence of mobile-phase and temperature effects on the gradient elution reversed phase chromatographic behavior of proteins. Using LiChrospher SI 500, bonded with n-butyl groups and a gradient in 1-propanol, 10 mM H3PO4, rapid separation and high mass recovery were obtained for a series of globular proteins. This protein separation and recovery are compared to those obtained when acetonitrile and acetonitrile plus 10 mM H3PO4 are used as eluting gradient solvents. In general, acetonitrile yielded lower recovery than 1-propanol, particularly for the more hydrophobic proteins, e.g., ovalbumin. For all three gradient solvents, little difference was observed in retention or recovery when the n-alkyl chain of the bonded phase varied. On the other hand, relative to the n-alkyl phases, a significantly lower retention of all proteins was found on more hydrophilic phases, e.g., cyano and nonendcapped n-butyl, when acetonitrile was the organic modifier, while in the case of 1-propanol, no retention difference was observed. Thus, column comparisons depend on the protein/mobile-phase combinations examined. The role of column temperature was also studied, and it was found that for certain proteins dramatic changes in peak shape occurred as a function of temperature. The influences of ionic strength and salt type were also studied. Protein mass recovery was shown to decrease with an increase in salt concentration; moreover, perchlorate was shown to have a larger effect in this regard than phosphate. In addition, salt concentration and type were found to influence peak shape greatly in certain cases. The results indicate the strong influences of mobile phase and temperature on chromatographic behavior, and some of the options available when this behavior is not satisfactory. Several protein separations are presented illustrating the power of the reversed phase approach.