Hyperventilation and ergonovine tests were carried out in a group of 30 patients with variant angina to assess the sensitivity of the 2 tests and to correlate the response with spontaneous disease activity. Hyperventilation produced a positive response in 83% (25 of 30) and ergonovine in 93% (28 of 30) of the patients. After hyperventilation 22 of 25 showed ST-segment elevation, 2 ST depression and 1 T-wave pseudonormalization; after ergonovine ST-segment elevation developed in 23 patients, ST depression in 4 and T-wave pseudonormalization in 1. In all cases the electrocardiographic changes occurred in the same leads as during the spontaneous attacks. The incidence of chest pain and ventricular arrhythmias was similar during both tests; spontaneous remission of ischemia, however, was more frequent (48 vs 14%) after hyperventilation than after ergonovine. Acute ischemia developed at a mean of 218 +/- 112 seconds after the end of hyperventilation in 19 of 25 positive tests; at that time double product was not significantly different from basal values. The sensitivity of hyperventilation was similar (95 vs 100%) to ergonovine in the patients with greater than or equal to 1 daily attack, while in those with less than 1 daily attack the sensitivity of hyperventilation decreased to 55% compared to 77% with ergonovine. Thus, in variant angina the sensitivity of both tests correlates with disease activity. Hyperventilation is a safe provocative test with a sensitivity similar to ergonovine in patients with active disease; however, in patients with sporadic attacks hyperventilation has a lower sensitivity than ergonovine and therefore a limited diagnostic value.