The relative bioavailability of cyclosporin A (CsA) from a new microemulsion oral formulation (NEO) and the currently used soft gelatine capsule (SGC) was determined at steady state in 12 patients with rheumatoid arthritis. The AUC(0,12 h) values of cyclosporin A were significantly greater after NEO than SGC (2873 +/- 848 ng ml-1 h (mean +/- s.d.) vs 2355 +/- 1128 ng ml-1 h; P = 0.02, 95% CI (confidence interval of the difference: 81 to 955 ng ml-1 h). Cmax values were significantly higher after NEO than after SGC (811 +/- 244 ng ml-1 vs 495 +/- 291 ng ml-1, P < 0.0001, 95% CI of the difference: 209 to 422 ng ml-1).