The assessment of fetal condition, in the presence of high risk factors, is aided "well being" tests. These tests attempt to screen for the possibility of fetal compromise and assist the followup of high risk gestations. One of the most commonly used tests is the nonstress test (NST), which is based on the interpretation of the resting fetal heart rate (FHR) tracing, and relates baseline FHR patterns to a prediction of fetal health. Application of knowledge engineering in the field of obstetrics resulted in the expert system NST-EXPERT, which evaluates and interprets NSTs, develops prognoses for immediate neonatal outcome and suggests clinical management strategies. To evaluate the system, 177 consecutive patients who underwent NSTs for common high risk problems were independently assessed by three perinatologists and expert system. The results obtained show that de diagnostic, therapeutic and prognostic abilities of NST-EXPERT equals or exceeds that of experienced perinatologists in this limited but unselected population sample. The results are not only encouraging, but may enable future incorporation of these types of systems into routime antepartum assessment.