Gull Laboratories, a Salt Lake-based medical diagnostic manufacturer, had sales of $921,966 in the third quarter of 1988, an 8 percent increase over the same period a year ago. The sales resulted in a $166,398 profit for the quarter.

In the first nine months of the year, the company showed $3 million in sales, a 23 percent increase over the same period a year ago. Profits for the nine months were $617,900, a 38 percent increase over the same period a year ago, company officials said.