I know this is a pretty much standard question regarding JS, and I understand that it probably has been answered several times before - I probably just suck at searching for the correct solution. I have an already made form on a website, where people can select different activities for a given timeframe. Some of these activities stretch over two or more given timeframes, and therefore, if one has selected the first one, it should not be possible to choose anything else for the second (and possibly, third drop-down). Example: Select 1: user selects "time-frame-two" Select 2: greyed out, with the same choice as in Select 1 Select 3: (if used) the same as Select 2 Example: Select 1: user selects "time-frame-one" Select 2: pulls the single-time actions from the database, and lets the user select one Select 3: same as Select 2 It should of course not be possible to select a time-frame-two from the second select-box if it's not already selected in the first select-box. The different activities stretching over more than one time-frame is also not singular - a user can usually chose between 3-4-5 different activities, which all stretch beyond the singular time-frame. And there is always single-time-frame possibilities. So. How do I do this? I would prefer to just add javascript-code to already existing form, if possible, I have full access to the webserver, so I can do mostly anything, and I would of course prefer to not change the PHP/MySQL too much, although adding needed ID-fields in tables etc. is no problem. Anyone have any tips, solutions, code I can look at, etc.? I really don't know JS much - HTML / PHP is fine, but I'd like to do this without the page having to refresh, and then... JS is the only way, it seems