| Acronym | Meaning |
| MRM | Multiple Reaction Monitoring |
| MRM | Multiresidue Method |
| MRNA | Messenger Ribonucleic Acid |
| MRO | Medium Range Order |
| MRP | Medical Removal Protection |
| MRP | Multidrug Resistance Protein |
| MRS | Materials Research Society |
| MRS | Magnetic Resonance Spectroscopy |
| MRS | Micro-Raman Spectroscopy |
| MRS | Minimum Required Strength |
| MRS | Monitored Retrievable Storage (for Radioactive Wastes) |
| MRSA | Methicillin-resistant Staphylococcus Aureus |
| MRSD-CI | Multireference Single And Double Excitation CI |
| MRSD-CI+D | MRSD-CI (with) Davidson Correction |
| MRSD-CI+P | MRSD-CI (with) Pople Correction |
| MRSI | Magnetic Resonance Spectroscopic Imaging |
| MRSPT | Modified Rayleigh-Schroedinger Perturbation Theory |
| MRT | Mean Residence Time |
| MRV | Mini Rotary Viscometer |
| MS | Mass Spectrometer |
| MS | Molecular Spinor |
| MS | Multiple Scattering |
| MS X(ALPHA) | Multiple-scattering X(alpha) Exchange Method |
| MS-RC(XI) | Multiple Scattering Relativistic Correlated (calcn. Method) |
| MS-RHFR | Momentum-space Restricted Hartree-Fock-Roothaan |
| MS/MS | Multistage Mass Spectrometry |
| MSA | Metropolitan Statistical Area |
| MSA | Microscopy Society Of America |
| MSA | Mineralogical Society Of America |
| MSA | Mammary Serum Antigen |
| MSA | Many-trajectory Semiclassical Approxn. (in At.-collision Theory) |
| MSA | Mean Spherical Approxn. |
| MSA | Methanesulfonic Acid (air Pollutant) |
| MSA | Multivariate Statistical Analysis |
| MSAE | Multistate Atomic Expansion (method For At. Collisions) |
| MSAPC | Mobile Source Air Pollution Control |
| MSBAR | Molecular Structure-biological Activity Relationship |
| MSBR | Molten Salt Breeder Reactor |
| MSC | Molecular Simulated Crystal Method (in Compton Profile Calcns.) |
| MSC | Multiplicative Scatter Correction |
| MSCE | Modified Semiclassical Exchange (aproxn. In Scattering Calcns.) |
| MSCET | Month And State Current Emission Trends |
| MSCV | Murine Stem Cell Virus |
| MSD | Mass Selective Detector |
| MSD | Mean Square Displacement |
| MSDS | Material Safety Data Sheets |
| MSEL | Materials Science And Engineering Laboratory |
| MSEP | Mean Square Error Of Prediction |
| MSF | Multi-stage Flash Distillation Plant |
| MSFA | Monosegmented Flow Analysis |