This paper reports on some bacteriological, ultrastructural, and biochemical features of dental plaque from children living in an area of Morocco, where the caries activity is low in spite of a high sucrose intake combined with the presence of copious amounts of plaque. The most numerous groups of bacteria found were streptococci, gram-negative facultative cocci, and staphylococci or micrococci. Streptococcus mutans, S. sanguis, S. salivarius, and enterococci were present in low numbers only. Other microorganisms encountered were Lactobacillus, Actinomyces, Veillonella, Bacteroides, and Fusobacterium. Attempts were made to classify spirochetes on the basis of their ultrastructural features. The general morphology of plaque was found to compare well with previous electron microscopic descriptions of old plaque. Gram-positive as well as gram-negative cocci, rods, filaments, and occasional spirochetes were seen embedded in a matrix of varying electron density. Aggregation between similar as well as dissimilar types of bacteria was noted. Structures probably representing glycogen, lipid, or polymetaphosphate inclusions were observed in many organisms. The composition of the plaque matrix was studied by protein and polysaccharide analyses of various plaque extracts.