If you know the compound Id (PCN, CN, LN or LnbRef) you can look for your compound just using the quick search on the Compound Registration navigation bar.
For a more advanced search, you can use the Search page. Here you can locate entries already stored in the registry database using a set of filtering options. A specific search could be used with the combination of the available search criteria. The search service also supports the use of chemical structures as queries. However, there are limitations here, e.g.: only 50 compounds are returned as hits at first (then at each scroll 50 more hits will become available from the bottom of the page); the substructure search might be very slow because of the large result set. Note also that Markush structures are stored in a separate table and the regular structure and the Markush tables are not interoperable.
For large data sets including millions of compounds or a smaller set but with lots of additional data, we recommend setting up a dedicated downstream system for searching, that can be supported by one of our JChem search engines. This will enable you to perform your searches with higher performance, while also separating the search process from your registration process, which could otherwise be a bottleneck due to the shared resources.