Background : Therapeutic plasma exchange is the therapeutic procedure to improve clinical course by removing various antibodies, immune complexes, toxic materials or by replacing insufficient plasma elements. But there are many debates about its effects although many immunologic diseases improve their clinical courses by plasma exange. The aim of this study is to examine clinical aspects of plasma exchange. Methods : We investigated retrospectively 30 patients who had been done a total of 128 plasma exchange procedures during the last 5 years at Korea University Anam Hospital. We judged clinical improvement according to diseases, replacing solutions and examined the changes of blood chemistries, side effects etc. Results : There were 14 males and 16 females. The patients' age ranged from 8 to 76 years old and mean age was 45 years old. Total 30 patients had been carried out a total of 128 plasma exchange procedures and the mean was 4.3 times. The frequency of plasma exchange was from once up to 12 times and five times is the most frequent number carried out (27%). The most frequent diseases were multiple myeloma and myasthenia gravis which were 17% respectively and other diseases in the decreasing order of frequency were hemolytic uremic syndrome (HUS), Guillian-Barre syndrome, fulminant hepatitis etc. Double lumen catheter into femoral vein(73%) was most frequently used for the vascular access. The clinical improvement was obtained in 50% of total cases and the clinical results in myasthenia gravis and Guillian-Barre syndrome were excellent. There were 8 patients(27%) who died during treatment period, but the cause of death was not related to plasma exchange procedure itself. As a replacement solution, 5% albumin alone(23%) was used most frequently and the others were fresh frozen plasma(FFP) alone(20%), FFP plus Hartman's soultion plus albumin(20%), FFP plus albumin(17%) etc. Serum total calcium concentration was significantly decreased from 8.5 to 7.9 mg/dL(p=0.017) and platelet was also decreased from 154,666/mm3 to 100,222/mm3(p=0.02) after plasma exchange but the other chemistries were not changed. The frequent side effects were nausea, vomiting, fever, chill, hypotension, itching sensation and muscle cramps. Conclusions : The plasma exchange is one of the useful therapeutic procedures in some immunologic diseases especially for the myasthenia gravis and Guillian-Barre syndrome. It is a relatively safe procedure, but gastrointestinal side effects such as nausea, vomiting in early period may be a problem. And the careful monitoring of serum calcium concentration, platelet count before and after plasma exchange is required.(Korean J Med 58:437-445, 2000)