After downloading the latest SOAP UI (5.2.1) on OSX El Capitan, it's just be hanging and unable to work. So I browsed the internet and found something that worked:
This fix was found at https://www.igorkromin.net/index.php/2015/05/05/change-the-jre-used-for-soapui-on-osx/ for a different issue.
Basically, SOAP UI is using a bundled JDK for 1.7, but I use JDK 1.8 - so we need to symlink it. Run the following:
cd /Applications/SoapUI-5.2.1.app/Contents/PlugIns/jre.bundle/Contents/Home mv jre jre.old ln -s /Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home/jre jre
Check that the symlink to your JDK is correct, versions might differ so it's worth checking. If you've got it wrong, SOAPUI will throw a startup error and tell you the JDK is missing.
Restart SOAPUI and all will hopefully be good!