Ge-films are evaporated under high vacuum conditions at 77°K. They are investigated either in the disordered state (before annealing at a higher temperature) or in the ordered state after annealing. The electric resistance R and the photoelectric work function Φ are measured before and after the influence of known amounts of carbon monoxide. R is plotted as a function of time and coverage n, Φ as a function of n. At 77°K an electronic interaction between the CO molecules and the Ge-film follows from an observed irreversible and reversible increase in R; Φ is not altered. The discussion by means of a band model shows that the CO molecules act as electron donors. At room temperature no interaction is found. Films precovered with oxygen show two simultaneous reactions during the adsorption of CO: a stronger adsorption on the spots precovered with oxygen and a weaker one on the bare Ge surface.