21-cm-line profiles of eleven open clusters and their immediate surroundings have been obtained showing line-emission of the clusters as well as that of the general galactic field. The expected profiles for the latter have been obtained in two, partially independent, ways, and substracted from the cluster profiles. The difference-profiles suggest in several cases the presence of interstellar neutral hydrogen gas within the cluster region. In a few cases the gas seems to expand with a velocity of about 7 km/sec. All clusters with an age of 2.5 · 107 years or less contain interstellar hydrogen gas while no clusters older than 1.5 · 108 years have detectable amounts of gas. The gas is found in a region which is, in the average, 3 to 4 times the apparent optical diameter.