Anthrax is a bacterial infection usually found in hoofed animals
Health officials have confirmed that anthrax has been found in a third heroin user in Glasgow.
The male patient is in a critical condition in the city's Royal Infirmary. Another patient there is also being tested for the infection.
A man and woman in the city's Victoria Infirmary tested positive for anthrax last week. The man died on 16 December.
Police and health officials believe contaminated heroin or a contaminated cutting agent may be responsible.
Dr Syed Ahmed, consultant in public health medicine, said: "I urge all drug injecting heroin users to be extremely alert and to seek urgent medical advice if they experienced an infection.
"Drug injecting is extremely risky and dangerous. The possible presence of a batch of heroin contaminated with anthrax makes drug injecting even riskier and even more dangerous.
"While this section of the community need to be on their guard the risk to the rest of the population - including close family members of the infected cases - is negligible."
Anthrax is an acute bacterial infection most commonly found in hoofed animals such as cattle, sheep and goats.
It normally infects humans when they inhale or ingest anthrax spores, but cannot be passed from person to person.
The last previous death from anthrax in Scotland was in 2006 when Christopher Norris died after inhaling the spores.
The 50-year-old craftsman, from Stobs, near Hawick, made drums with materials such as untreated animal hides.