Increasing concerns over the environmental fate of plant nutrients applied for agricultural production has stimulated research examining several management practices that may improve nutrient use efficiency thereby minimizing the potential for environmental contamination.  Among the management practices being studied is the use of enhanced efficiency (EE) fertilizers.  These fertilizers, which include slow release fertilizers and other older or relatively new fertilizer technologies, have not been extensively tested for their effects on environmental losses of plant nutrients under agronomic crop production.  This paper will review the processes by which EE fertilizers may reduce potential environmental contamination and also examine some current research that has compared gaseous and leaching losses of nitrogen (N) after application of conventional and EE fertilizers under a range of edaphic and climatic conditions.  In general, the results of this research indicate that climatic conditions have a large influence on observed differences in environmental losses between conventional and EE fertilizers.  For example, a two-year study in Missouri comparing polymer-coated and conventional urea fertilizers under different drainage and irrigation treatments showed few differences in plant growth after application of the two fertilizer sources but differences in nitrous oxide flux and nitrate concentration of water samples collected in suction lysimeters were observed during the relatively wet first growing season, but not consistently in the relatively dry second growing season.  These and other results suggest that both agronomic and environmental assessments of EE fertilizers are needed to determine the value of these products for their possible in-field and off-field effects that are important to both agricultural producers and society as a whole.