Astaxanthin is primarily used as a food supplement in the aquaculture industry, which over the past twenty years has experienced tremendous growth. A complex synthetic process produces almost all of the astaxanthin sold, and consequently, the selling price is very high. Thus a bioprodn. process of astaxanthin may be economically attractive, and in addn. would have the added advantage of being an \"all natural\" product. The yeast Phaffia rhodozyma is the only known yeast that simultaneously produces the carotenoid pigment astaxanthin and metabolizes simple carbohydrates. The wild strain produces low levels of the pigment, though through mutation/genetic modification economically attractive levels of astaxanthin are produced. Up until now, few studies have been conducted in continuous culture under precisely defined conditions. In this work, three P. rhodozyma strains (one wild and two mutants) have been characterized under stationary and dynamic growth conditions. Metabolic flux models are being developed to locate bottlenecks in the carotenoid biosynthesis pathway. [on SciFinder (R)]