The systemic effects of timolol eye drops were investigated in 35 patients divided into three groups: 1. (15 asthmatics); 2. (10 non-asthmatic patients suffering from glaucoma); 3. (10 elderly control subjects). A placebo eye drops was given at time 0, the timolol maleate drops were given at time 30 mn. The control parameters were checked every 15 minutes. They did not show variations under placebo. After administration of timolol, systolic and diastolic blood pressures as well as vital capacity remained unchanged. Heart rate decreased in 91% of subjects by a mean: 18.5% and, extreme 38%: Bradycardia was always sino-atrial and there was a dose effect relationship. Also F.E.V., decreased in 13 of the 15 asthmatics and in 2 patients with chronic bronchitis: in 4 patients the decrease in flow exceeded 20%. The importance of timolol in the treatment of open-angle chronic glaucoma is well-established, but the results reported here and else where emphazing frequent risks should induce prescribers to comply with the rules of good use: analysis of previous history, and compliance with general contra-indications to beta blockers. Routine E.C.G. and strict adjustment of dosage is recommended.