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Surface‐enhanced Raman spectra of various molecular gases adsorbed on colloidal matrix isolated silver, sodium and potassium clusters of about 100 Å diameter are reported. For CO adsorbed on silver clusters the strongest enhancement is observed in the region of considerable surface plasmon absorption of the metal colloid (electromagnetic enhancement). N2 and O2 adsorbates on silver colloid on the other hand show much weaker SERS‐signals. Furthermore the frequency shift of the adsorbate relative to the condensed free molecule as well as the line broadening is much weaker than for CO, indicating a weaker chemical interaction. – The importance of surface plasmon excitation for getting SERS signals is additionally proven by using colloids of sodium and potassium. On these more reactive metal colloids chemical reactions can even be monitored at low temperatures.