Two food surveys determined the areas of consumption and the ethnic groups involved as well as the way and motivations for using Spirulina algae (Oscillatoria platensis) in Chad. More than 400 homes were visited in February (dry season) and October (end of the rainy season and period after the millet harvest). Consumption is limited to a restricted proportion of the population in the Kanem region. Among the Kanembu group (the leading consumers of Spirulina), frequencies of use vary between one and six melas out of ten. The amounts consumed per person during a meal, in the sauce accompanying millet, are between 9 and 13 g. Variations in consumption linked to ethnic, social and seasonal factors are discussed. With regard to food value, the very high proportion of sand considerably reduces the protein content in the product sold on the market. An average ration of sauce containing "diĕ" helps cover about 10 to 12 p. 100 of the protein requirements of an active adult man, and the algae by themselves contribute 5 to 8 p. 100 of these requirements. A comparison with the leading sauces consumed in Kanem reveals no superiority for Spirulina.