When he arrived at work at the BBC World Service offices, Markov noticed a small red pimple had formed at the site of the sting he had felt earlier and the pain had not lessened or stopped. He told at least one of his colleagues at the BBC, Theo Lirkov, about this incident. That evening he developed a fever and was admitted to St James' Hospital in Balham, where he died four days later, on 11 September 1978, at the age of 49. Dr. Bernard Riley, the attending physician treating Markov, considered many possible causes of his illness, including that Markov had been bitten by a poisonous tropical snake. Dr. Riley had the inflamed area at the back of Markov's leg x-rayed, but no foreign object was detected at this time.