TomK, in the same fashion that you're constantly checking for a button press (which should be happening with every loop), you can also read in serial data and pass it on to the LED being lit. Where things get complicated is when you have multiple LEDs going at the same time (when the button was pressed multiple times). Now you have to read enough serial data for all of the LEDs. How does your serial device (sending the data) knows how many LEDs are on? Does it send one set of data, or does it send multiple? What's the purpose of this serial input?