High counting rates from 125I in radioimmunoassays.

Responses from one manual and four automatic gamma counters for assaying (125)I were compared. The resolution times quoted by manufacturers when applied in a standardized correction formula to obtain true counts from observed counting rates above 10(4) counts per second appeared to be inadequate. The need to investigate the errors associated with high counting rates for all instruments and electronic settings employed to determine (125)I in radioimmunoassays is emphasized.