[en] An attempt was made to measure In-111 labeled platelet survival time rapidly in a total of 31 patients with thrombopenia or thromboembolism. Mean platelet survival time and maximum platelet recovery were obtained when platelet radioactivity decreased by 10-19% (L-method), by 20-39% (M-method), and by 40-59% (S-method). Using the conventional L-method as standard, mean platelet survival time was classified as normal (8 days or more), slightly shortened (4-7 days), or extremely shortened (less than 4 days). In the normal group, mean platelet survival time obtained by S-method significantly differed from that by L-method, although there was no difference between M- and L-methods. In the other slightly shortened and extremely shortened groups, there was no significant difference in survival time among the three measurement methods. Regarding maximum platelet recovery and measured maximum, there was no difference among the three measurement methods. It appeared that the S-method is feasible when platelet radioactivity decreases by less than 70% on the 2nd day of measurement; and that the M-method is feasible in the other cases. In measuring platelet survival time, it seemed possible to reduce the measurement days by 1-2 days for the normal group, 1-4 days for the slightly shortened group, and 2-4 days for the extremely shortened group. (N.K.)