The effects of anticoagulant solutions on the recovery of transfused platelets were studied. Citrate anticoagulants at pH 7.4 or pH 6.5 were found to be equally effective in preserving the viability of platelets when centrifugation of the cells was not required. When centrifugation is required, as in most platelet survival studies, citrate at pH 6.5 gives maximum recoveries. Ethylene diamine tetraacetate (EDTA) caused temporary sequestration of nearly all transfused platelets and reduced maximum recoveries by about 50 per cent.

Platelet recovery was lowered by ABO-incompatibility between donor platelets and recipient serum, but survival time of remaining platelets was not altered. Lowest platelet recoveries resulted when group A₁ or A₁ B platelets were given to group O recipients with high isoagglutinin titers.

It is suggested that ABO-compatible platelets prepared in citrate should be used where possible in the treatment of thromboctyopenic disorders.