To provide convenient usage, the MiCroKiTS 4.0 database web interface was designed in a user-friendly manner for search and browse. The website contains four search options including one/multiple keywords-based simple search, ‘Advanced search’ based on a combination of multiple keywords, multiple keywords based ‘Batch search’ and protein sequence-based ‘BLAST search’. For example, if a keyword ‘aurora’ in ‘Any Field’ was submitted for a simple search , the website will return a list of MiCroKiTS proteins, such as Aurora kinase B from H. sapiens in a tabular format with accession, species, and protein/gene names/aliases . By clicking the accession ‘Q96GD4’, user could visit the webpage of human Aurora kinase with detailed annotation including localizations, PubMed IDs of source references and the orthologs . For human MiCroKiTS proteins, the representing fluorescent microscope figures were provided by clicking the ‘Show Figures’ . Furthermore, two terms specified in two areas and combined with operators of ‘and’, ‘or’ and ‘exclude’ could be employed to perform a complex query in ‘Advanced Search’ . For example, querying the database with ‘human’ in ‘Species’ and ‘aurora’ in ‘Gene/Protein Name’ will return three human aurora kinases . Alternatively, user could submit a list of keywords to perform a batch search. For example, three human aurora kinases could be retrieved by submitting the list of their UniProt accessions . Furthermore, user could submit a protein sequence in FASTA format in ‘BLAST Search’ to find homologous MiCroKiTS proteins . For example, the sequence of human Aurora kinase B could be input in the FASTA format to search homologous proteins in the database. The ‘Advanced Search’, ‘Batch search’ and ‘BLAST Search’ will return the list of searching hits in a tabular format as the simple search. In addition, there is a checkbox of ‘ONLY experimentally identified MiCroKiTS proteins’ for each search option. If the checkbox is selected, only experimentally identified MiCroKiTS proteins will be queried.