We have constructed a database system named CHRONIS (CHROmosome and Nano-Information System) to collect images of animal chromosomes and related nanotechnological information. CHRONIS enables rapid sharing of information on chromosome research among cell biologists and researchers in other fields via the Internet. CHRONIS is also intended to serve as a liaison tool for researchers who work in different centers. The image database contains more than 3,000 color microscopic images, including karyotypic images obtained from more than 1,000 species of animals. Researchers can browse the contents of the database using a usual World Wide Web interface in the following URL: http://chromosome.med.niigata-u.ac.jp/chronis/servlet/chronisservlet. The system enables users to input new images into the database, to locate images of interest by keyword searches, and to display the images with detailed information. CHRONIS has a wide range of applications, such as searching for appropriate probes for fluorescent in situ hybridization, comparing various kinds of microscopic images of a single species, and finding researchers working in the same field of interest.