This research investigated whether ergot alkaloids associated with endophyte-infected tall fescue could alter plasma concentrations of pituitary hormones that regulate biological processes related to cattle performance. Seven Angus yearling steers received single i.v. injections of ergotamine tartrate, ergonovine maleate, or saline vehicle in a simple cross-over design. Each steer was given a different compound each week. Blood samples were collected at 15-min intervals for 45 min before and 240 min after treatments to assess plasma concentrations of prolactin, growth hormone, and LH. Respiratory rates were measured hourly to ascertain a systemic effect. Ambient temperature averaged 34 degrees C during data collection. Treatment x time was a significant source of variation for respiration rate and plasma concentrations of each hormone evaluated. Respiration rates were higher for ergonovine than for saline (P < .02) and ergotamine (P < .07) 30 min after treatment, but they were higher (P < .05) for ergotamine than for ergonovine and saline by 210 min after treatment. Both alkaloids transiently elevated (P < .01) plasma growth hormone concentrations compared with before alkaloid treatment and after saline treatment. Ergotamine reduced (P < .01) plasma concentrations of prolactin and LH throughout the 120-min period after treatment compared with concentrations before ergotamine treatment and after saline treatment. Ergonovine lowered (P < .01) prolactin concentrations for a shorter time than ergotamine and did not affect mean LH concentrations. Results indicated that ergot alkaloids implicated as contributing agents to fescue toxicosis can alter plasma concentrations of pituitary hormones important to cattle production.