Current metered dose inhalers (MDIs) contain chlorofluorocarbon (CFC) propellants. A new propellant HFA134a, with no effect on ozone, may be a suitable alternative. Four asthma medications, salbutamol, salmeterol, fluticasone propionate (FP) and beclomethasone dipropionate (BDP), currently containing standard CFC propellants, were formulated with HFA134a for investigation. Single doses of salbutamol (200 micrograms) and salmeterol (50 micrograms, 100 micrograms) provided equivalent protection against bronchial provocation, after histamine and methacholine respectively, compared with the current preparation. A double-blind 4 week study comparing the two formulations of salbutamol, used as required in mild to moderate asthma, showed similar effects on morning peak expiratory flow rates (PEFR) and inhaler use. Salmeterol (50 micrograms) twice daily was compared with the current formulation in a 4 week trial. Improvement in morning PEFR was similar for both formulations. A double-blind study compared the two formulations of FP (250 micrograms) twice daily in moderate asthmatics previously taking 400-1,000 micrograms of inhaled corticosteroid daily. Morning PEFR improved in both groups. Safety and tolerability of the HFA134a product were similar to current formulations. The HFA134a formulations of salbutamol, salmeterol and FP provide equivalent efficacy with a similar safety profile to the existing formulations at equivalent doses.