AIMS: The purpose of this pilot study was to test whether the rate of collagen synthesis is measurable in the aqueous humour samples in reoperated and previously unoperated eyes. METHODS: The material consisted of 28 eyes of 27 patients, aged 5 to 82 years, in whom aqueous humour samples were obtained during eye surgery. Fifteen patients had no history of previous eye surgery (control group) while 12 patients were re-operated (study group). The carboxyterminal propeptide of type I procollagen (PICP) and the aminoterminal propeptide of type III procollagen (PIIINP) were measured by specific immunoassays in the aqueous humour samples. RESULTS: The mean concentration of PIIINP in the study group (8.4 (SD 12.5) micrograms/l) was statistically significantly larger than that of the control group (0.4 (0.4) micrograms/l) (p < 0.0037). The respective values for PICP were 98.8 (SD 177.7) micrograms/l in the study group and 0.7 (SD 2.8) micrograms/l in the control group (p < 0.0005). The eyes in the study group which were re-operated within 1 year showed values increased 20-fold compared with the eyes in the control group and those eyes in the study group which had had their previous operation more than a year ago. In three eyes aqueous humour samples were also obtained from the encapsulated Molteno bleb and showed values increased 12-fold compared with those from the anterior chamber. CONCLUSIONS: PICP and PIIINP immunoassays are suitable for measuring the rate of collagen synthesis in the aqueous humour and may be useful in studies on pharmacological modulation of wound healing in glaucoma surgery.