That skin color matters in societal interaction is a given; that it influences the kind of treatment you receive in hospitals is the startling conclusion of a new study.

Doctors participating in the study were given an identical set of symptoms affecting two people, both aged 50. The symptoms clearly invited the diagnosis of heart attack.

ABC News reports that the doctors were likely to prescribe clot-busting treatment for one of the patients, but not the other -- the difference being that the one benefiting from the potentially life-saving treatment was white, the other black.

Real people were not used in the study; the doctors saw computer-generated images on a monitor.

Once the doctors had evaluated the two simulated patients, they were given an 'implicit association test'' designed to reveal a person's unconscious views of blacks and whites.

"If you scored high on the bias against African-Americans portion of the test, then you were actually less likely to provide clot-busting treatment for a heart attack for black patients," ABC News quotes Massachusetts General Hospital's chief researcher Alexander Green as saying.

The stronger a doctor's anti-black feelings, the less likely he or she would be to give the black patient the clot-busting agent that is considered one of the most effective treatments for such symptoms.

The study, by the Disparities Solutions Center, an affiliate of Harvard University and Massachusetts General Hospital, suggests that unintentional racism, in the form of feelings the physicians are even unaware of, affects how doctors diagnose and treat patients.

The study, published in the online edition of the Journal of General Internal Medicine, is the first to deal with racial bias, and how it could lead to inferior care for African-American patients.

"Physicians, like others in the US, in this country, demonstrated unconscious biases based on race," ABC News quotes Green as saying.

ABC News quotes Dr Albert Morris of the National Medical Association as saying this isn't the first study to find that whites get better medical care than blacks. However, Morris is quoted as saying the latest study differs from previous ones in that it demonstrates for the first time that the reason for differential care is skin color.

Interestingly, the study found that even black doctors showed bias against black patients, though less frequently than white doctors.