Introduction Various investigators reported pronounced effects of the age ofmyceHal mats of various fungi on their growth, metabolism and enzymic activities. Thus, the reductase contents of mycelia of Aspergillus niger was reported by Rossi (1929) to decrease with age. TAMIYA and YASUSABURO (1929) found that young myeelia of Aspergillus sp. were richer in zymase. PROSKV~Z~KOV (1936) observed that glyeerophosphatase extracted from young mycelium of Aspergillus oryzae was much more active than that extracted from an equal weight of older mats. ROU~ET and Z~LL~,a (1945) reported a diminution of the rate of production of diamine oxidase by Mycobacterium smegmatis with age. FowDn~ (1952) has found that culture age of Chlorella vulgaris had little effect on the protein composition when they were grown in media containing ammonium and nitratenitrogen. So~oKI~ in 1957 studied the course of respiration during the life cycle of Chlorella cells and found that in the course of autotrophic growth, the respiration increases rapidly, reaches a maximum and then undergoes a slow decline. The present investigation was planned with a view to studying the growth, respiration and nitrogen metabolism with special reference to protein synthesis by mycelial mats of Fusarium culmorum of different ages as affected by varying the nitrogen sources in the culture media.