Temperature, pH, enzymes and ions affected the two types of [~3H]tyrosine binding sites differently. The optimal temperature and pH for the high affinity sites were 24 C and 7.4, and for the low affinity sites 37℃ and 7.0, respectively. The [~3H]tyrosine binding to the high and low affinity sites was not observed at 55℃, nor at pH 6.0 or pH 8.5. Trypsin reduced [~3H]tyrosine binding to the high affinity sites, but had no effect on the binding to the low affinity sites. Neuraminidase reduced [~3H]tyrosine binding to the low affinity sites, but had no effect on the binding to the high affinity sites. None of cycloheximide, kCG, cAMP, and progesterone affected [~3H]tyrosine binding. The optimal temperature and pH for the high affinity sites were 24 C and 7.4, and for the low affinity sites 37 ° C and 7.0, respectively. The [~ 3H] tyrosine binding to the high and low affinity sites was not observed at 55 ° C, nor at pH 6.0 or pH 8.5. Trypsin reduced [~ 3H] tyrosine binding to the high affinity sites, but had no effect on the binding to the low affinity sites. Neuraminidase reduced [~ 3H] tyrosine binding to the low affinity sites, but had no effect on the binding to the high affinity sites. None of cycloheximide, kCG, cAMP, and progesterone affected [~ 3H] tyrosine binding .