IL2 production in response to phytohemagglutinin (PHA) was measured in 5 patients with growth hormone deficiency (GHD) (ages 7.8-14.5). In 3 patients IL2 was determined before and 24 hrs after the first dose (2 units) of human growth hormone (HGH) administration. In 2 patients IL2 was measured after 1 and 16 months of HGH treatment. At no time could IL2 production be identified in these patients. In contrast 1 patient (age 14) with short stature and normal GH responses to standard stimulatory tests on treatment with exogenous HGH for 6 months did produce IL2 normally.We have previously presented data (Society Pediatric Research 1984) demonstrating that continuous treatment with HGH for 1 year resulted in transient decrease in % B cells, T helper/suppressor (T H/S) ratio and PHA responsiveness in 8 GHD patients. When treatment was interrupted for 1-2 month intervals, restarting HGH resulted in a fall in % B cells in 5/7 patients, mean 17.6% (range 12-20) to 7.8% (range 6-11) and a fall in T H/S ratio in 4/7 patients, mean 1.83 (range 1.5-2.0) to 1.20 (range 1.0-1.4) after 1-2 months of treatment. Serum immunoglobulins and poly-morphonuclear leukocyte function was not affected by HGH treatment for up to 24 months in any patient.In conclusion Interleukin 2 production, unlike other immune parameters, is impaired in growth hormone deficient patients and is unaffected by human growth hormone treatment.