Medical Specialists Associated 5461 La Sierra Drive Dallas, TX 75231 (At the corner of La Sierra and Manderville.) 214-692-8541 Office Hours 24 Hour on Call Services Monday - Friday 7:30 AM to 5:00 PM Closed Saturday and Sunday Lab Hours Monday - Friday 7:15 AM to 4:30 PMOur Team‧CORONA VIRUS (COVID-19) ALERT‧Services and Procedures‧Jones‧Dr. Moss‧Dr. Gist.