The D(-) isomer of lactic acid appears to cause a form of metabolic encephalopathy experienced by patients who have jejunoileal bypass for morbid obesity. However, analysis for D(-)-lactate is not routinely available in clinical or reference laboratories. We describe an enzymic centrifugal-analyzer assay for D(-)-lactate in plasma or serum, with use of D(-)-lactate dehydrogenase. The method involves two-point kinetic calibration and preincubation of specimen and NAD+, thus eliminating the need for specimen-blanking or protein-precipitating pretreatment. This rapid, accurate, and precise assay should be helpful in evaluating patients with 'short-bowel syndrome' who display confusion, lethargy, ataxia, or other central nervous-system disturbances that may be ascribable to D(-)-lactic acidosis.