In a group of 19 rheumatoid arthritis (RA) patients with normal renal function, serum levels of aluminium (AlS) were monitored during treatment with drugs containing this metal (Al). The AlS levels during treatment were significantly higher (0.005 less than p less than 0.01) than those before treatment, i.e. 19.4 (SEM 2.3) micrograms/l and 12.3 (1.7), respectively. This increase in AlS was significantly (0.025 less than p less than 0.05) correlated with the pretreatment serum creatinine level (mean value for the whole group 80.5 (SEM 4.7) mumol/l) but showed no correlation with the predicted creatinine clearance. Although the increase in AlS during therapy with A1 containing drugs is not dramatic in RA patients with normal renal function, the rheumatologist should be aware of the risk of increased AlS concentration in RA patients, especially those with impaired renal function.