Abstract: As new compounds are now provided N-methyl-3-(3,4-dihydroxyphenyl)serine alkyl esters which are effective as an .alpha.-adrenergic and .beta.-adrenergic agent to stimulate the .alpha.-adrenergic and .beta.-adrenergic functions of the central nervous system of mammalian animals and are expectable to be useful for therapeutic treatment of disorders as invoked by reduced biological activities or functions of the .alpha.- and/or .beta.-adrenergic neurons. N-methyl-L-threo-3-(3,4-dihydroxyphenyl)serine (C.sub.1 -C.sub.6) alkyl esters are preferred amongst the new compounds of this invention.