I am seeking some advice about letters of recommendation. It seems msny MSTP and MD/PhD programs require atleast two different letters from people who can attest to your lab experience. I know in some big labs, multiple PhDs or PhD/MD's might be in a lab. However, I volunteer in a small lab. My PI is a PHd and she is going to write a LOR for me but is a LOR from a graduate student in my lab or a post-doc acceptable? If a post-doc/grad student LOR is unacceptable, should I plan on working in a different lab in order to get another letter from a PI? Any suggestions would be appreciated.