The stability of human coronavirus 229E infectivity was maximum at pH 6.0 when incubated at either 4 or 33 degrees C. However, the influence of pH was more pronounced at 33 degrees C. Viral infectivity was completely lost after a 14-day incubation period at 22, 33, or 37 degrees C but remained relatively constant at 4 degrees C for the same length of time. Finally, the infectious titer did not show any significant reduction when subjected to 25 cycles of thawing and freezing. These studies will contribute to optimize virus growth and storage conditions, which will facilitate the molecular characterization of this important pathogen.