Faecal carriage rates for antibiotic-resistant Escherichia coli were determined in a Dutch urban population during two periods with an interval of seven years. In the period 1978-1980 faecal samples were collected from 624 persons and in 1987 from 154 persons. E. coli was isolated from samples of 577 persons in the first period and from samples of 125 persons in the second period. The frequency of E. coli-carrying persons found with tetracycline-resistant E. coli decreased from 42% in 1978-1980 to 20% in 1987 (p less than 0.001). The frequency of persons with a predominantly tetracycline-resistant E. coli flora (greater than 50% of the E. coli flora resistant) decreased in the period 1978-1980 from 12% to 6% in 1987 (p less than 0.05). There was an increase in frequency of persons found with a predominantly ampicillin-resistant E. coli flora from 5% in 1978-1980 to 11% in 1987 (p less than 0.01). Antimicrobial resistance in the open population is a dynamic process. Data concerning an association with antibiotic consumption are mostly lacking. Further intervention studies on the influence of antibiotic policies are needed.