The validity of radioimmunoassays of each of luteinizing hormone, follecile stimulating hormone, prolactin, thyroid stimulating hormone and insulin was assessed from the point of view of iodinated tracer purity of one type of commercial clinical radioimmunoassay kits. The use of high resolution gel filtration made it possible to purify further the standard iodinated tracers. Comparative radioimmunoassays using the unpurified preparations and the purified fractions enabled the detection of overestimations as well as underestimations of standards and unknowns in all the investigated hormones, together with non-specific binding effect noticed with the use of the unpurified iodinated preparations.