A study was conducted to determine whether chronic exposure of ewe lambs to the electric and magnetic fields (EMF) of a high-voltage ac transmission line affected cortisol secretion and growth. Twenty Suffolk ewe lambs were assigned randomly in equal numbers to a control and treatment group. Treatment from 2 to 10 mo of age consisted of continuous exposure within the electrical environment of a 60-Hz, 500-kV transmission line (mean electric field 6 kV/m, mean magnetic field 40 mG). Treated lambs were confined directly beneath the transmission line; control lambs were maintained in a pen of similar construction 229 m from the line where the EMF were at ambient levels (mean electric field < 10 V/m, mean magnetic field < .3 mG). Cortisol was analyzed by RIA in serum of blood samples collected at .5- to 3-h intervals over eight 48-h periods. All ewe lambs were weighed weekly and side-patch wool growth was measured biweekly. Cortisol secretion occurred in a circadian rhythm; daytime serum concentrations were greater (P < .05) than nighttime concentrations for both groups. Concentrations of cortisol did not differ between the control and exposed ewe lambs. Weight gain and wool fiber length and diameter also were not affected by treatment. These data suggest that chronic exposure of developing ewe lambs to 60-Hz environmental EMF does not affect concentrations of cortisol secretion, body weight gain, and wool growth.