The skin reactivity and lymph node responses to a large scale of different doses of oxazolone, were followed under continuous stimulation for a period of 12 days. It was found that the lack of a continuous high blast cell activity in the paracortex was a physiological response that could be observed with high dosage as well as with very low dosage. Low doses gave distinct stimulation of the paracortex without any detectable reaction in the cortex and in the medulla. Manifest stimulation of these compartments required considerably higher doses. A marked paracortical response was the only lymph node change required for development of a typical delayed type skin response. When germinal centres and plasma cells had developed, the skin reactivity was also found to change characteristically.