In the last few years many reports have been published concerning shortened platelet half-life in different diseases such as atherosclerosis and hematological disorders. Up to the present moment, however, there is no information available concerning age and sex dependency in healthy people. Therefore, we evaluated platelet half-life in 106 patients, who had been examined because of a suspected atherosclerotic or hematological disorder having been excluded in the sequel. In all the patients we found negative bicycle ergometry and negative sonography of the carotid arteries and the legs. Platelets were labelled with 100 muCi of 111Indium-oxine-sulfate at 37 degrees C for 5 minutes. The mean labelling efficiency was 90%, the recovery about 70% after two hours. We found a statistically significant correlation (r = -0,5395; p less than 0,001 between age and platelet half-life. In male patients we observed a trend towards shortened platelet half-life, however, the differences were not significant.