IN RESPONSE TO SEVERAL REQUESTS FOR UNIFORM LABELED NUCLEOTIDES, WE HAVE EXAMINED THE EFFICIENCY OF SEVERAL POSSIBLE METHYLOTROPHIC BACTERIA FOR THE CONVERSION OF [13C]METHANOL INTO NUCLEIC ACIDS. UTILIZING THE RUMP STRAIN METHYLOTROPHUS METHYOPHYLUS AS1, WE HAVE OPTIMIZED THE YIELD OF RIBONUCLEOTIDES AND DURING GROWTH IN A STANDARD FERMENTOR. EACH LITER OF OUR GROWTH MEDIUM CONTAINS 4 G OF METHANOL AND YIELDS 1 GRAM OF LYOPHILIZED CELLS. WE HAVE ISOLATED AN AVERAGE OF 170 MG OF RNA PER GRAM OF LYOPHILIZED CELLS. THE RNA IS DIGESTED ENZYMATIC ALLY TO YIELD A MIXTURE OF RIBONUCLEOSIDE MONOPHOSPHATES. THE NUCLEOTIDES MONOPHOSPHATES ARE SEPARATED BY CHROMATOGRAPHY ON DOWEX-1 IN THE ACETATE FORM. FROM THE SAME LABELED CELLS, WE HAVE ISOLATED DNA, ENZYMATICALLY DIGESTED IT AND SEPARATED U- 13C AND U-15N LABELED 2-DEOXYNUCLEOTIDES MONOPHOSPHATES. [U-15N]ADENOSINE MONOPHOSPHATE AND [U-15N]GUANINE MONOPHOSPHATE HAVE BEEN PROVIDED TO USERS.