|Abstract||The albino mutant strain in the woodlice, Armadillidium vulgare, was investigated with respect to the yellow patterns on the dorsal integument. Pigment cells were observed with electron microscope in order to determine the cell types of yellow markings. Quantitative analyses of pteridines in the albino were carried out by HPLC. The result indicated that the albino integument contain sepiapterin, biopterin, pterin, isoxanthopterin as in the wild type and the red mutant strain. The total amount of the four pteridines in the albino was about half as much as that in the red phenotype for both males and females, respectively. Males and females showed almost the same totals and ratios of the four pteridines in the albino and red phenotypes. Therefore, pteridine contents in both phenotypes of A. vulgare may not be related to the activity of androgenic gland hormone. Yellow chromatophores of the albino and red phenotypes were morphologically identical, emitting a yellow fluorescence. These cells contained numerous electron-lucent pigment organelles which were similar to pteridine granules of the wild type.