The haematological and clinical data in 254 Italian subjects with beta-thalassaemia trait are reported. 46% of the patients were anaemic, 40% complained of weakness, 19% showed enlargement of the spleen and 10% enlargement of the liver. The haemoglobin levels ranged from 8 to 15.5 g/dl with a normal distribution and a mean of 12.73 for males, 10.93 for females and 11.34 for children (4-15 years). Reticulocyte counts and serum bilirubin levels were slightly increased and both showed a statistically significant relationship with haemoglobin levels. The serum iron level was increased in 27% and decreased in 6% of the cases. Haemoglobin A2 concentrations ranged from 3.5% to 8% with a normal distribution and a mean of 5.37; Hb F values were less than 1% in 36% and varied from 1 to 14% in the remainder. Red cell osmotic fragility was decreased in all but 6% of the subjects: low MCV, MCH and MCHC values were observed in 75%, 86% and 10% respectively. A comparison is made between the data and those obtained by other workers.