Apple chief executive Steve Jobs is taking medical leave, two years after taking a six-month break when he underwent a liver transplant, sending Apple stock tumbling on Monday.
Jobs, a survivor of pancreatic cancer, said chief operating officer Tom Cook would take responsibility for day-to-day operations but he would continue to be chief executive.
"At my request, the board of directors has granted me a medical leave of absence so I can focus on my health," Jobs, 55, wrote in an email to staff. "I love Apple so much and hope to be back as soon as I can."
Apple shares fell 8.3% in Frankfurt. Monday was a holiday in the United States and markets were closed there.
Apple has been closely identified with the charismatic Jobs, who revived the computer maker's fortunes in 1996 after a 12-year absence from the company he co-founded.
Analysts said the effect on Apple's operations should be limited in the short term, since its product line-up was strong, but his absence would be a worry if it became prolonged. Cook ran day-to-day operations during Jobs's last absence in 2009.