The dependence of the coercive force of Ni, Fe, and Ni&sngbnd;Fe films upon film thickness and amount of trapped gas was evaluatedin vacuo. The magneto‐optic Kerr effect was utilized for this investigation. Although the penetration depth of light into the film material was determined to be 150±25 A, measurements ofHccould commence for film thicknesses <100 A. It was found that the coercive forceHcis independent of film thickness if the content of trapped gas, as indicated by thep/r(residual gas pressure over deposition rate) ratio is very small, e.g., 5×10−8torr/A/sec for Ni films. At higherp/rratios, the coercive force of Ni films displays initially a steep rise which is followed by a shallow minimum, while in Ni&sngbnd;Fe films a maximum appears at about 750 A. The different behavior of Fe films is ascribed to higher gas absorption on this material rather than a principal change in the mechanism of the coercive force. A hypothesis is proposed as explanation for the observed effects.