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IN a previous communication Sahasrabudhe (1958) put forth evidence in support of existence of a chemical competition between nucleic acid and py-ridine nucleotide syntheses for the appropriation of a common precursor, adenine. In a rapidly growing malignant tissue, adenine was shown to be appropriated for nucleic acid synthesis and very little was left for incorporation in pyridine nucleotides (Narurkar, Kumta and Sahasrabudhe, 1957). It was further show-n that the pyridine nucleotide levels were invariably lowered in presence of rapid nucleic acid synthesis irrespective of whether it (the nucleic acid synthesis) was of neoplastic or non-neoplastic origin (Jedeikin, Thomas and Weinhouse, 1956 ; Kotnis, Narurkar and Sahasrabudhe, 1959). Pyridine nucleotides have an important role in the hydrogen transport system and thus indirectly participate in the production of energy, via the tricarboxylic acid cycle. In view of this it was suggested that low levels of pyridine nucleotides automatically slow down all the synthetic and proliferative activities by controlling the energy production. Based on these ideas, a biological feed-back mechanism was postulated for the regulation of normal growth processes (Sahasrabudhe, 1958). In'tumour tissue however, this feed-back-mechanism seems to break down; the tumour apparently is able to obtain an unhmited supply of energy to maintain its rapid nucleic acid synthesis. A search for an alternate pathway capable of producing energy independent of the proposed feed-back-mechanism revealed that hexose-monophosphate pathway (HMP) has the requisite potentiality of not only producing energy (though not yet definitely established) but also yielding ribose-5-phosphate which is the starting material for the biosynthesis of purines. In the light of this the reported preponderance of HMP pathway in tumour tissue acquires greater significance (Kit, 1956; Kit and Graham, 1956; van Vals, Bosch and Emmelot, 1956). Interference of HMP pathway, it was thought, would inhibit the tumour growth by curtailing the supply of energy and ribose-5-phosphate. This has been attempted by preparing anti-metabolites against some suitable intermediates of the HMP pathway.An ideal chemotherapeutic substance has to have prefere'ntial action on tumours only, with no or minimuni action on the host tissues. It was this consideration which prompted us to rule out the possibility of useful results with anti-meta-

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