SYNOPSIS. Recent advances in the cellular aspects of chromatophoric activities in fishes are reviewed, special emphasis being laid on the black pigment-containing cells, the melanophores. A few recent electron-microscopic studies have disclosed the fine structure of melanophores. They are enclosed with a single cell membrane, within which melanosomes and other cell organelles are found. All observations favor the view that melanosomes are selectively moved through the cellular processes, leaving the cell contour rather fixed. In regard to these findings, current ideas about the mechanisms of pigment movements are discussed. Particular attention is directed to the possible intervention of microtubules and the theory of migration of pigment by intracellular electrophoresis. The regulatory mechanisms of pigment cells are then dealt with. The adrenergic nature of transmission is affirmed in the peripheral melanin-aggregating nervous system. The mode of nervous supply to a melanophore is also analyzed. Investigations of the antagonistic, melanin—dispersing, nervous system are also considered, with special reference to recent physiological studies and to the finding of synaptic vesicles by electron microscopy. On the basis of these results, a new interpretation of the so-called Parker effect is proposed.