The relationships between spontaneous variations in serum 24-h osteocalcin (OC), carboxyterminal propeptide of type I procollagen (PICP), and aminoterminal propeptide of type III procollagen (PIIINP) concentrations and GH secretion, measured as GH response to provocative pharmacologic stimuli and spontaneous GH secretion during 24 h, were evaluated in prepubertal normal children and in GH-deficient and GH-secreting short normal children (SNC). All the subjects showed a circadian rhythm in smoothed 24-h OC and PICP mean data with higher nocturnal values in comparison with diurnal values. Conversely, serum PIINP concentrations did not vary throughout the day. In children with classic GH deficiency and nonclassic GH deficiency, mean 24-h serum levels and smoothed 24-h mean data for OC, PICP, and PIIINP were significantly reduced (p < 0.001) with respect to age-matched controls. SNC showed mean 24-h OC concentrations similar (p = NS) to those we found in age-matched controls, but they had significantly lower (p < 0.001) diurnal 12-h mean data in comparison with controls. SNC also showed both 24-h PICP and PIIINP mean data and smoothed 24-h PICP and PIIINP mean data significantly lower (from p < 0.02 to p < 0.001) at all the time points of measurement in comparison with controls. Twenty-four-hour PICP and PIIINP mean data were positively related to spontaneous 24-h GH concentrations (r = 0.77, p < 0.005 and r = 0.69, p < 0.005, respectively) and growth velocity (r = 0.85, p < 0.005, and r = 0.70, p < 0.005, respectively), whereas 24-h OC mean data were not.(ABSTRACT TRUNCATED AT 250 WORDS)