Plasma from six chronically catheterised sheep fetuses of 113–126 days conceptual age showed high levels of corticotrophin at all ages with somewhat higher values towards term. Plasma cortisol was not clearly related to corticotrophin in individual samples but was highly correlated in the pooled data. Short bouts of hypoxia (5–10 min 10% O2 in N2 to the mother) produced no significant change in either corticotrophin or cortisol although small transient changes in PO2 and lactate occurred. The high levels of corticotrophin suggest that the possibility of stress in the chronically catheterised preparation must be considered.