Heavily T2-weighted spin echo sequences of the brain show age-dependent low signal intensity in many extrapyramidal nuclei. Although it has been suggested that this low intensity results from non-haem iron, the specific influence of non-haem iron on the T2 relaxation time has not been quantified and remains controversial. The T2 relaxation times of the globus pallidus and putamen were measured from MRI at 1.5T in 27 healthy patients, by using a mathematical model. They were then plotted as a function of age and compared to the curve of age-dependent iron concentration determined post mortem. The curves of T2 relaxation time in the basal ganglia are congruent with published curves of iron concentration, indicating a high probability that the changes in T2 relaxation times and the low signal in the basal ganglia result from the local, age-dependent iron deposition. Individual measurements of T2 relaxation time show less variation before than after 45 years of age, indicating the influence of a second, more individual factor.