Adapting continuous culture techniques for the measurement of micro-nutrient effects upon algae growth has been shown to be a satisfactory method. Several refinements and modifications of previously utilized equipment for the study of algae macro-nutrient uptake made it possible to test the effects of molybdenum upon Scenedesmus quadricauda. However, with the progressively reduced substrate levels of molybdenum two problems became increasingly apparent: Molybdenum contamination of the media by magnesium sulfate approached or surpassed the experimental levels in the dilution cultures and prevented the attainment of a molybdenum deficient control; and The extremely low substrate levels of molybdenum could not be detected by the neutron activation analysis due to interference by the high phosphate concentrations in the media. However, the analyses were useful where either the phosphate concentrations were low (lake water and reagent chemicals) or molybdenum concnetrations were relatively high. (Author)