Caffeine is increasingly used as a biochemical probe for liver function, in cancer epidemiology, and in pharmacogenetics, with its recognized ability to assess the activities of CYPlA2, xanthine ox&se, and N-acetyltransferase-2. The activity of tbese hepatic enzymes was tested in 45 Shona children from a rural area of Zimbabwe with use of caffeine as a probe. Many of these rural black children had lower indexes of CYPlA2 activity than otherwise on our extensive records; the average value (3.78 + 2.9) was significantly @ < 0.001) lower than that of healthy white urban children firorn Zimbabwe (8.86 -C 3.36) or from Canada (7.92 & 1.88), or that of healthy Canadian adults (5.96 + 2.4). A higher CYPlA2 activity in children than in adults is usual. The low CYl?lA2 activity of the children from rural Zimbabwe calls for medical studies and suggests a widespread and perhaps serious impairment of certain liver functions. Causes could be parasitic infections with Scb&osomu mnsmi, causing scbistosomiasis, wbicb are endemic, in addition to generally poor nutrition and tiequent iodine deficiency. By contrast, the xanthine oxidase activity in rural Shona children was slightly higher than that reported for a healthy Canadian adult population. The N-acetyltransferase activities were comparable in both the rural and urban chiIdren and were also similar to those reported in a population study of healthy adult Canadians. (CLIN PHARMACOL hR 1995;57:25-31.