For the past few years, the Canadian Apheresis Study Group has collected data on most apheresis procedures carried out throughout the country. The information accumulated during calendar year 1985 has been reviewed, and the complications that occurred as a result of therapeutic plasma exchange (PE) have been assessed. There were side effects during 612 (12%) of the 5235 procedures done, involving 252 (40%) of the 627 patients treated. The most common reactions were fever, chills, urticaria, muscle cramps, or paresthesias; these reactions were encountered more frequently when plasma was used in the replacement fluid. Most reactions had little or no clinical significance. However, there were 28 severe complications, including one cardiac arrest and two respiratory arrests. Five late deaths occurred, but these were not related directly to PE. Although PE is relatively safe, life-threatening reactions do occur, and patients require careful observation during the procedure.