According to the experimental model of a 5 X 5 Latin square, 5 treatments were studied single blind in 5 patients, affected by stable-effort angina, by means of exercise tests. In the period of maximal supposed effect the following treatments were investigated: placebo (P), 1 tablet, orally; isosorbide dinitrate (ISDN), 5 mg, sublingually; propranolol (Pr), 40 mg, orally; nifedipine (N), 10 mg, orally; verapamil (V), 160 mg, orally. Placebo, compared with its own control tests, did not change any of the examined parameters. Comparison of the 'active' treatments with P showed the following results. All the treatments increased the duration of work before ECG positivity appearances. An increase in duration of work and total work performed before angina was seen after administration of ISIDN, N and V; the improvement observed after treatment with Pr was not significant. Comparison of treatments showed that work performance before angina was the same after administration of ISDN, N and V; these treatments were more effective than that with 40 mg Pr. Duration of work before ECG positivity was significantly longer after ISDN and N than after Pr. The changes in heart rate, maximal arterial pressure, ejection time index and triple product confirmed the activity of the administered doses. According to the observed effects on exercise tolerance, in comparison with P the same level of work was performed with the same triple product after Pr, and with lower triple products after ISDN, N and V.