To explore the possible utilization of goldfish scale in monitoring environmental toxicants as well as that for calcified tissue research, characteristics of cells in the scale were examined by identifying genes differentially expressed in those cells. Subtraction cloning was subjected to RNAs between scale-gill (SG), gill-scale (GS) and scale with lateral line-scale without lateral line (LS). Total numbers of 4, 6, and 9 clones were isolated respectively from SG, GS and LS pools. Blast search of their sequence showed only low homology to other fish sequences so that 5' rapid amplification of cDNA (5'RACE) was applied to the obtained 5' terminal side of each sequence. Among 19 clones, LS3 alone showed the high homology to zebrafish nucleosome assembly protein 1 (NAP1) and the rest of 18 was not yet identified. In situ hybridization confirmed that faint expression of NAP1 mRNA was observed in cells along the ridge of the scale without lateral line. On the other hand, in small cells not along the ridge of the scale with lateral line, very intense hybridization was found as expected. They were abundant at the surrounding area of the lateral line tube. NAP1 plays an enhancing role on gene expression by promoting nucleosome assembly. Thus, cell viability in the scale with lateral line seemed to be higher than that in the scale without lateral line. The scale can be a good model to monitor the effects of environmental pollutants because simultaneous observation against cells with different cell viability is available through comparison between cells in the scale with or without lateral line.