The difference between living with HIV and dying of AIDS is more than a matter of semantics. For several years after infection - whether through sex, needles or blood - most people have no obvious health problems. Eventually, little things start to show up. After three or seven or, more typically, 10 years, serious infections and cancers start to break through the HIV-ruined immune system. That final stage is what we call AIDS.

Doris Butler found out her own ailing son was infected with HIV when he was just 13 months old. Butler - who'd once had a relationship with an intravenous drug user and who'd also had a transfusion - knew right away that she must have infected the baby. But she, her husband and teen-age daughter did not discuss that fact for a full year.

One of them, 47-year-old filmmaker Peter Adair, has made a documentary about what it means to be HIV positive. Absolutely Positive - showing tonight on PBS and this week at the Seventh International Conference on AIDS in Florence, Italy - promises to be an eye-opener for those who assume HIV positive means nothing but grief.