Knowledge of the circadian patterns of serum IGF-II and the large molecular weight IGF binding protein, IGFBP-3 might, apart from its physiological relevance, be of clinical interest, inasmuch as measurements of these parameters are being introduced into the evaluation of GH deficiency. We therefore evaluated the 24-h (08.00-08.00 h) patterns of serum IGF-II and IGFBP-3 in 8 GH-deficient patients who were studied during three periods when receiving 1. GH (2 IU) at 20.00 h; 2. GH (2 1U) at 08.00 h and 3. no GH. For comparison, 10 age- and sex-matched untreated healthy subjects were studied once under similar conditions. The serum IGF-II levels of the patients were relatively stable over the 24-h periods, yielding mean levels which were significantly lower during no GH: 553 +/- 78 (evening GH), 554 +/- 54 (morning GH), and 429 +/- 65 micrograms/l (no GH). The mean IGF-II level in the normal subjects was 635 +/- 29 micrograms/l, which was significantly higher than in either patient study. Similarly, stable 24-h levels of IGFBP-3 were recorded in all studies. The mean IGFBP-3 level of the patients was significantly lower when they received no GH, and the mean level in the healthy subjects was higher than in any of the patient studies: 1853 +/- 301 (no GH), 2755 +/- 317 (evening GH), 2904 +/- 269 (morning GH), and 3856 +/- 186 micrograms/l (healthy subjects). However, minute but significant changes over time, characterised by slight decrements at night, were observed for both parameters in several of the studies.(ABSTRACT TRUNCATED AT 250 WORDS)