A research project sponsored by Uni-Bell PVC Pipe Association dealing with the fatigue strength of PVC (polyvinyl chloride) pipe was recently completed at Utah State University. The objective of the project was to develop an improved design methodology for predicting fatigue failure of 6-inch PVC pipes. The tests completed during this effort focused on fatigue failure at lower stress amplitudes. The test results show that the design criteria based on work by previous researchers is very conservative, particularly if the stress amplitude is small. New curves for predicting fatigue failure are presented. The results are very applicable to design engineers working on municipal water systems. Includes 7 references, tables, figures.