If you think your valued collection of DVD movies will last a lifetime, think again - some are already starting to wear away while others are falling apart.

Unofficial estimates put the number of affected DVDs at between 1 and 10%. Yet some of the main distributors for Hollywood Studios are accused of rejecting to accept the problem exists and replace defective products.

The technology, sold as a replacement for VHS, with added interactive contents, is now five years old and the DVD industry claims it is the most triumphant packaged media in consumer electronics history. The failures are a combination of corrosion - known as "DVD rot" - and delamination, where the layers of the disc separate.

Last year Australians spent $398 million buying 13.3 million DVD movie titles - a three-fold increase on the 4.3 million sold in 2001, according to research firm GFK.

Symptoms of the rot include picture break-up and freezing at a specific place on the dvd. The major cause is believed to be poorly planned cases. Delamination shows up as a coffee-like stain that inhibits the disc from playing. Among those worst affected are video movie rental stores, which buy millions of titles per year.

Rohan Byrnes, 34-year-old science fiction fanatic who owns 350 DVD movies, has spent a lot of time glaring at DVD rot. He works as a failure analysis engineer, with access to an optical microscope.

Mr Byrnes has studied five cases of DVD rot - four in his own compilation - and suspects the microscopic decay spots on the aluminium layer inside the disc could be caused by a "chemical attack", possibly linked to the glue used.

"Some stores have reported they only get two or three rentals from a DVD before it's unplayable," said Ross Walden, director of the Australian Video Retailers Association. Distributors "are washing their hands of it", he said. "Once a DVD has been rented out [distributors] will not take them back."

One DVD movie website lists 18 titles known to have at least one bad batch, among them Planet of the Apes (1968), Men in Black: Collectors Edition , Independence Day and the Alien Legacy box set.

Mr Byrnes returned his discs to the distributors, 20th Century Fox and Columbia TriStar, including his analysis, and got replacements, but other victims were not so fortunate. Peter Longworth, a DVD collector in Newcastle, had an identical problem with Planet of the Apes two years after buying it.

However, 20th Century Fox declined to replace it as it was out of the 90-day warranty.

"The company declined to accept that there was a manufacturing setback," he said. Mr Longworth wrote to the Australian Competition and Consumer Commission in November, but the movie rental watchdog does not act on consumer warranty problems.

Meanwhile, 20th Century Fox refused to comment on the subject. A spokesman said only: "We always fully compensate our customers for any manufacturing liability found." Warner Home Video's managing director, Stephen Nickerson, said: "If a customer has trouble with a disc and it is obviously a manufacturing problem we will replace it. The question is whether it is caused by a manufacturing problem or consumer abuse."