The effects of halothane on maternal and fetal hemodynamics, distribution of fetal cardiac output, regional cerebral blood flow, and fetal cerebral oxygen consumption were studied in the ewe (N = 9) using radionuclide-labeled microspheres. An adjustable uterine artery occluder was used to produce a controlled state of fetal asphyxia. Measurements were taken during three periods of study: 1) control, 2) asphyxia, and 3) asphyxia plus 15 min of 1% maternal halothane. The fetal cardiovascular response to asphyxia was acidosis, hypoxia, hypertension, bradycardia, and preservation of vital organ blood flows. There was a significant drop in maternal blood pressure when halothane was administered but uterine blood flow was maintained, 308 ml X min-1 during asphyxia versus 275 ml X min-1 with halothane. Fetal blood pressure during asphyxia plus halothane (54 mmHg) was significantly lower than that during asphyxia alone (59 mmHg), while heart rate was significantly higher: 172 beats per minute (bpm) versus 125 bpm (P less than 0.05). Despite these changes, the administration of halothane during asphyxia did not produce a reduction in vital organ flows. Cerebral blood flow was maintained: 357 +/- 37 ml X 100 g-1 X min-1 during asphyxia alone and 344 +/- 26 ml X 100 g-1 X min-1 after halothane administration (P = NS, mean +/- SEM). Cerebral oxygen delivery also was maintained: 8.3 +/- 0.8 ml X 100 g-1 X min-1 during asphyxia alone versus 9.7 +/- 1.5 ml X 100 g-1 X min-1 after halothane, compared with 11.2 +/- 1.1 ml X 100 g-1 X min-1 during the control period.(ABSTRACT TRUNCATED AT 250 WORDS)