The specificity of the assay method for the gonadotrophin inhibiting factor (gif) has been studied in two ways. In the first part of the study the biological activity of various gonadotrophin preparations remaining after heating at 100°C for 1 hr was measured. In the second part the effect of these hormones on the bio-assay method for the gif was investigated.
Following heating it has been shown that most, but not all, of the biological activity of the preparations studied is destroyed when assayed by specific methods. Gonadotrophins derived from ovine pituitary tissue, but not from human urine, have been demonstrated to be capable of causing a uterine response in the assay for the gif.
It is concluded that the assay method for the gif is not specific. For this reason care must be taken in interpreting the results of assays of the gif in clinical situations in which high endogenous gonadotrophin levels are likely to be present.