Clas Svahn of UFO Sweden said the group opened its archives in Norrkoping, Sweden, to the general public for only one day Sunday, Swedish news agency TT reported Monday.
Svahn said about 70 people took advantage of the opened archives.
"There was a great interest," he said.
The UFO group held a series of lectures Saturday in the opening of the archive.
"One hundred seventy-five came to listen and there was a great interest. There were more than we have seen in recent years and there was a serious interest. We are very happy," he said.
Among the cases available for public viewing Sunday was a report of a Swedish pilot who spotted an unidentified object floating in the water during a training exercise in the 1970s. The report says the object flew straight up into the air and the pilot was unable to catch up. The object was never identified.