Pyridoxal analogues can be useful for treating B.sub.6 deficiency and related diseases; cardiovascular and related diseases; melanoma and related diseases; and symptoms thereof. One such analogue is a compound of the formula: ##STR00001## or a pharmaceutically acceptable acid addition salt thereof, in which R.sub.1 is alkyl, alkenyl, in which alkyl or alkenyl can be interrupted by nitrogen, oxygen, or sulfur, and can be substituted at the terminal carbon by hydroxy, alkoxy, alkanoyloxy, alkanoyloxyaryl, alkoxyalkanoyl, alkoxycarbonyl, or dialkylcarbamoyloxy; alkoxy; dialkylamino; alkanoyloxy; alkanoyloxyaryl; alkoxyalkanoyl; alkoxycarbonyl; dialkylcarbamoyloxy; or aryl, aryloxy, arylthio, or aralkyl, in which aryl can be substituted by alkyl, alkoxy, amino, hydroxy, halo, nito, or alkanoyloxy. These analogues can be administered, either alone or concurrently with known medications, to treat the above-described diseases.