About 100 pickled brains have gone missing from an American university, leaving professors scratching their heads.

Officials at the University of Texas, in Austin, believe students may have stolen the organs, which are preserved in jars of formaldehyde, for Halloween pranks or to use as bizarre ornaments.

The brain of alumni Charles Whitman, the sniper who shot 46 people and killed 16 in a notorious massacre on the campus in 1966, is believed to be among the specimens that have disappeared.

“We think somebody may have taken the brains, but we don't know at all for sure,” psychology professor Tim Schallert, the co-curator of the collection, told the Austin American-Statesman.

His co-curator, psychology Professor Lawrence Cormack, said the missing brains were half of the university’s collection.

“It's entirely possible word got around among undergraduates and people started swiping them for living rooms or Halloween pranks,” he added.

A local hospital transferred the brains to the university almost 30 years ago under a temporary possession agreement.

Half were put in Mr Schallert’s psychology lab but there was only room for 100 so the rest were moved to the basement of the university's Animal Resources Centre. But they are no longer there.

A spokesperson for the University of Texas said the “circumstances surrounding this collection since it came here nearly 30 years ago" will be fully investigated and that officials are "committed to treating the brain specimens with respect".

He added that the remaining brain specimens on campus are used "as a teaching tool and carefully curated by faculty”.

The university's agreement with the hospital required it to remove any information that might identify the person from whom the brain came.

But Mr Schallert said Whitman's brain likely was part of the collection.

“It would make sense it would be in this group. We can't find that brain,” he added.

He killed 16 people including his mother and wife in the rampage, mainly from the observation deck of the University of Texas Tower, before he was shot dead by police.

Whitman reportedly wrote in his journal that he wanted an autopsy to be conducted on his body to determine if there was a biological reason for his actions and increasing headaches.

A brain tumour was found that doctors believe could have influenced his emotions and he was taking psychostimulant Dexedrine at the time.

The 100 remaining brains have been moved to the Norman Hackerman Building, where they are being scanned with high-resolution resonance imaging equipment.