We evaluated the Amerlite system (Amersham, Bucks, UK) for hCG and FT4. The within-run imprecision (CV%) for hCG was 4.05 at 19.6 U/l (n = 10), 6.28 at 43.45 U/l (n = 10) and 4.62 at 298.57 U/l (n = 10). The between-run imprecision (five replicates for ten days) was 4.8%, 15% and 11%, respectively. The system was linear up to 200 U/l. A good correlation between Amerlite hCG and an IRMA assay (Becton Dickinson, r = 0.91), Delfia (Pharmacia, r = 0.91) and an automated ELISA assay on ES 600 (Boehringer, r = 0.92) was observed on 70 samples. Within-run imprecision for FT4 was 3.8% at 0.7 ng/dl (n = 10), 3.3% at 1 ng/dl (n = 10) and 4.32% at 5.15 ng/dl (n = 10), and between-run was 5.95%, 4.4% and 8.2%, respectively. The comparison with a commercial direct RIA (Becton Dickinson) showed good correlation (r = 0.90, n = 100 samples). The diagnostic value of the association of thyrotropin and FT4, in comparison with the traditional thyroid tests (T3, T4, thyrotropin, FT4, FT3) has been assessed in various thyroid diseases.