Summary In order to validate results obtained in ‘acute’ versus ‘chronic’ experimental conditions, two fetal sheep nutrients, lactate and glucose, have been determined in ‘acute’ conditions and compared with the ‘chronic’ data in the literature. Maternal and fetal blood glucose in ‘acute’ conditions was in the range of published ‘chronic’ data. Fetal blood lactate was similar in ‘acute’ and during ‘chronic’ conditions. Maternal and fetal veno-arterial (VA) differences were in the same direction in ‘acute’ and in ‘chronic’ conditions for both lactate and glucose and of the same magnitude for lactate. For glucose, a good relationship was observed between umbilical VA differences and maternal arterial concentrations for all ‘acute’ and ‘chronic’ values. Thus no fundamental differences appear in the results obtained in ‘acute’ or during ‘chronic’ conditions. The applicability of such animal results to the human and the use of acute conditions to study fetal nutrition in the human are discussed.