It was found that with neonatally induced transplantation tolerance about 50% of the rats are insensitive, or little sensitive, to the adoptive transfer of immunity. The proportion of rejected and unrejected skin grafts in individual experiments did not show a direct dependence on the dose of transferred cells, and immune lymphocytes were as effective as non-immune cells. No dependence on the time post-transplantation was found. Only the results of the adoptive transfers performed after more than 120 days after transplantation indicated an increased resistance of the tolerant state. Also repeated transfers in which increasing doses of cells were used showed a relatively stable state of tolerance in some animals. It is discussed that the difference in the sensitivity to the adoptive transfer might reflect at least quantitative individual differences in the mechanism of the state of unresponsiveness in neonatally induced tolerance.