Serum concentrations of the markers of collagen synthesis and degradation, collagen I propeptide (PICP), collagen III propeptide (PIIINP) and the cross-linked telopeptide of type I collagen (ICTP) were measured in young male dermatological patients and in control subjects. No significant differences were noted between patients suffering from atopic eczema (n = 24), other eczemas (n = 11), acne (n = 8), psoriasis (n = 7) or tinea (n = 9) and the control subjects (n = 24). In the total study population representing patients with common skin diseases and control subjects there was a significant correlation between the serum concentrations of PICP and PIIINP and between the concentrations of PICP and ICTP. This suggests that synthesis of type I and III collagens in vivo is coordinated and that the degradation and synthesis of type I collagen is balanced. These markers were also measured in older patients suffering from psoriasis, eczema and various connective tissue diseases. It was noted that the degree of skin involvement in these diseases was not related to the serum concentrations of the markers of collagen metabolism. The highest levels of PICP and PIIINP were observed in a patient with systemic mastocytosis (PICP 309 micrograms/l and PIIINP 8.0 micrograms/l). Increased levels of PIIINP were also found in patients with a high alcohol consumption. We have previously demonstrated that systemic glucocorticoids reduce collagen propeptide levels in serum. In the present study we also proved that systemic glucocorticoids have no effect on collagen degradation.(ABSTRACT TRUNCATED AT 250 WORDS)