Thirteen puerperal women with insufficient lactation were treated with thyrotrophin releasing hormone (TRH) 20 mg twice daily for two weeks. Intravenous (iv) TRH stimulation tests were done before the TRH therapy and within 3-5 h after the last dose of oral TRH. Plasma samples were assayed for prolactin (Prl), thyrotrophin (TSH), triiodothyronine (T3) and thyroxine (T4) by radioimmunoassays, and the lactational response was objectively monitored in 11 women. Oral TRH treatment was associated with significantly (P less than 0.05) depressed Prl levels (23.0 +/- 7.9 microgram/l vs. 61.4 +/- 26.2, mean +/- SEM), no change in TSH levels (3.7 +/- 0.4 IU/l vs. 4.0 +/- 0.4) but significantly (P less than 0.01) elevated T3 (2.17 +/- 1.14 nmol/l vs. 1.83 +/- 0.09) and T4 (131.6 +/- 7.9 nmol/l vs. 96.6 +/- 5.8) levels. Oral TRH entirely blocked the TSH response and significantly (P less than 0.01) blunted the Prl response to iv TRH stimulation. No improvement in lactation was observed.