SJL mice exhibit a strain-specific age-dependent delay in the maturation of delayed-type hypersensitivity (DTH) responsiveness. They do not attain "adult" levels of DTH responsiveness until the 10th week of age, which is 4 to 6 weeks later than the other strains of mice tested. In this report we demonstrate that spleen cells, resident peritoneal cells and thioglycollate-elicited peritoneal exudate cells are all able to transfer DTH responsiveness from naive 12-week-old DTH responders to 6-week-old nonresponders. Transfer prior to immunization was more efficient at eliciting a response than transfer after immunization. As few as 5 X 10(4) cells from 12-week-old SJL mice can adoptively transfer responsiveness to unresponsive 6-week-old animals. The active cell was found to be adherent, radiation (2000 rds) resistant, I-A+, Thy-1- and Mac-1+. I-A compatibility between the adoptively transferred population and the nonresponder mice is required. These data suggest that young adult SJL mice lack a functional population of antigen-presenting cells specific for DTH and that the appearance of these cells is under maturational control.