Two patients who were receiving home parenteral nutrition complained of vague neurological symptoms of such severity that they underwent full clinical appraisal. The only positive finding was that plasma manganese concentrations were greater than twice the upper 95% confidence interval of normal (7-27 nmol/l). In the light of this result all nine patients receiving home parenteral nutrition underwent evaluation for possible manganese toxicity. One other patient had serum manganese concentrations exceeding twice the upper limit (127 nmol/l). The three patients with elevated serum Mn had evidence of manganese deposition in the brain on magnetic resonance imaging scanning. In contrast two patients with normal plasma results had negative scans. Patient susceptibility appears very variable. We suggest that current amounts of trace elements provided in nutrition solutions may be a potential source of nutrient activity. The fine tuning of supply and demand may be difficult on account of a limited range of commercially available trace element solutions.