The histological and biochemical characteristics of cacao (Theobroma cacao) endosperm were determined at different stages of seed development. At various stages, the endosperm was analysed for minerals, organic acids, carbohydrates, free amino acids, abscisic acid (ABA), indole-3-acetic acid (IAA) and cytokinins. Cacao endosperm was coenocytic and became progressively cellularized from the micropylar zone. From stage I to IIz, the endosperm started to degenerate all around the embryo. Among the minerals detected, potassium and sulphate were the most abundant. Ammonium was the major source of mineral nitrogen, and glutamine was the most abundant free amino acid. Total nitrogen concentration was quite low. No sulphur-containing amino acids could be detected. Malate was present at all endosperm stages and was the most abundant organic acid. The sugars in cacao endosperm were mainly reducing sugars: glucose and fructose. ABA was only detected from stage IIz. IAA and three cytokinins [zeatin, zeatin-riboside and isopentenyl adenosine (iPA)] were present at all stages of development. Cacao endosperm resembled the endosperm of other species in (1) the abundance of organic acids and phosphate; and (2) a unique combination of sugars. However, three features seemed to be specific to cacao: (1) nitrogen was supplied mainly in the form of ammonium and amino acids, whereas, in other species, amino acids represent the predominant form; (2) there was a relatively small amount of nitrogen, and (3) a high concentration of sulphate and the absence of sulphur amino acids.