| Acronym | Meaning |
| MELAS | Mitochondrial Myopathy |
| MELISA | Multianalyte Enzyme-linked Immunosorbent Assay |
| MELODRAMA | Melding Of Spin-locking Dipolar Recovery At The Magic Angle |
| MEM | Maximum Entropy Method |
| MEMOSA | Microelectromechanical Optical Sensor Array |
| MEMPT | Many-electron Many-photon Theory (in Dynamic-polarizability Calcns. For Atoms And Ions) |
| MEMS | Microelectromechanical Systems |
| MEMTB | Many-electron Mol. Tight-binding (for Electronic Structures) |
| MEN1 | Multiple Endocrine Neoplasia Type 1 |
| MEOR | Microbially Enhanced Oil Recovery |
| MEP | Matrix Effective Potential (for Scattering Calcns.) |
| MEP | Molecular Electrostatic Potential |
| MEP | Multiple Extraction Procedure |
| MEPAS | Multimedia Environmental Pollution Assessment System |
| MEPC | Marine Environment Protection Committee |
| MEPED | Medium Energy Proton & Electron Detector |
| MEPSAG | Minimum Energy Path Semiclassical Adiabatic Ground-state (tunneling Approxn.) |
| MERD | Metal-enhanced Reductive Dehalogenation |
| MERD | Mine Emergency Responsiveness Development |
| MERIE | Magnetically Enhanced Reactive Ion Etching |
| MERIS | Medium Resolution Imaging Spectrometer |
| MERLIN | Multi-element Radio-linked Interferometer Network |
| MERRF | Myoclonic Epilepsy Associated With Ragged-red Muscle Fibers |
| MERT | Medical Emergency Response Team |
| MERT | Microelectrical Resistance Tomography |
| MERT | Modified Effective-range Theory (for Electron-mol. Scattering) |
| MES | 2-(N-morpholino)ethanesulfonic Acid |
| MES | Methyl Ester Sulfonates (surfactants) |
| MES | Molecular Emission Spectroscopy |
| MESA | Mass Concentration Extinction Size Analyzer |
| MESA | Maximum Entropy Spectral Analysis |
| MESA | Mesoscale Self-assembly |
| MESFET | Metal Semiconductor Field-effect Transistor |
| MESI | Membrane Extn. With A Sorbent Interface |
| MESIMS | Matrix-enhanced Secondary Ion Mass Spectrometry |
| MESIP | Modeling Environmental Scenarios In Ponds |
| MESNA | Sodium 2-mercaptoethane Sulfonate |
| MESP | Molecular Electrostatic Potential |
| MESQUAC-MO | Mixed Electrostatic Quantum Chemical Calculation-MO |
| MET | Many Electron Theory (for Singlet Ground State) |
| MET | Multichannel Eikonal Theory (in Atom Electron-impact Excitation) |
| METAALICUS | Mercury Experiment To Assess Atmospheric Loading In Canada And The US |
| METC | Morgantown Energy Technology Center |
| MEUF | Micellar Enhanced Ultrafiltration |
| MEUG | Minimum Energy Uncertainty Gaussian (wave Packets) |
| MEV | Mink Enteritis Virus |
| MEVVA | Metal Vapor Vacuum Arc |
| MEXA | Multiple-energy X-ray Absorptiometry |
| MEXH | Multiple-energy X-ray Holography |
| MF | Membrane Filtration |