Additional USART question

I encounter a problem now and hope you all can help me out.
Im using USART interrupt to receive the coming in message. after i received the message from communication, i need to continuously blink a led till another USART interrup communication message come in to stop the led blink or continue blink.
but i found out that if i continue in the blinking sub-routine and a message come in from RS232 communication, my program will hang there and not function at all.
is there any other solution for this blinking and USART?
thanks ya.