Polyethylene glycol has been in use for a number of years for the assessment of gut permeability. The methods so far employed are usually limited to polyethylene glycols in the low relative molecular mass range (up to M(r) 1300). We developed a method for the simultaneous determination of gut permeability to M(r) 400, M(r) 1500, M(r) 4000 and M(r) 10,000 polyethylene glycol, by applying a single oral dose of an appropriate mixture of these polyethylene glycols. After extraction from 24 h-urine, M(r) 1500, M(r) 4000 and M(r) 10,000 polyethylene glycol were quantified by size exclusion chromatography, while M(r) 400 polyethylene glycol was determined by reversed phase chromatography. The detection limit of polyethylene glycol in the relative molecular mass range between M(r) 1500 and M(r) 10,000 was found to be 0.2 mg/l urine, and the detection limit of M(r) 400 polyethylene glycol 5 mg/l urine. Recovery of the polyethylene glycols (N = 6) were 86.6% (CV: 4.8%) for M(r) 400, 94.1% (CV: 7.2%) for M(r) 1500, 97.1% (CV: 5.5%) for M(r) 4000 and 97.4% (CV: 5.6%) for M(r) 10,000. No significant difference was found between the excretion rates in 24 h-urine of M(r) 400 and M(r) 1500 polyethylene glycols in patients with Crohn's disease (M(r) 400: 34.4 +/- 5.5%; M(r) 1500: 5.22 +/- 2.27%; mean +/- SEM, N = 10) and healthy controls (M(r) 400: 33.6 +/- 3.2%, M(r) 1500: 1.09 +/- 0.26%; N = 21). The excretion rate of M(r) 4000 polyethylene glycol was markedly higher in patients with Crohn's disease (0.462 +/- 0.177%) than in healthy controls (0.049 +/- 0.012%, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)