Cn3D macromolecular structure viewer
Downloading Cn3D for Macintosh

Note: As an alternative to downloading the Cn3D software using the links below, a web-based 3D structure viewer is available. iCn3D ("I see in 3D") is a WebGL-based viewer for interactive viewing of three-dimensional macromolecular structures and chemicals on the web, without the need to install a separate application. Read more on the About iCn3D page and the iCn3D Help document.

  System requirements:
i386 (Intel) CPU, running OSX 10.6 or higher
Download Cn3D 4.3.1 here:

Simply download the archive via this link, and extract it into a folder on your system, wherever you normally put application software, using your favorite zip archive application.

Once done, see the instructions for configuring your browser.
Note for Gatekeeper-enabled Macs (OSX 10.7.5 and up):
Solving the "unidentified developer" problem: If you encounter the message "Cn3D can't be opened because it is from an unidentified developer" when installing or running Cn3D, it is very likely the OSX "Gatekeeper" software is the cause. Apple has provided instructions you can follow to exempt Cn3D from Gatekeeper at, specifically, in the section "How to open an app from a unidentified developer and exempt it from Gatekeeper."
Note for running Cn3D on MacOS (OSX 10.15 and up):
In order to run Cn3D on MacOS versions OSX 10.15 and up, users need to install a replacement for the X11 windowing system, such as the open-source version of the X.Org X server XQuartz
The previous version, Cn3D 4.3, also continues to be available:

Revised 13 August 2020