A US company, T Cell Sciences, has developed a cheaper and easier diagnostic test for people infected with AIDS. Called TFAx CD4, the test measures levels of critical white blood cells, known as CD4 cells, that steadily decline in people with HIV. Current techniques are not only expensive, but can only measure I blood sample at a time, which must not be more than 2 days old (Science, Vol 268, No 5215).

The new method, which will soon hit the US market, can test several blood samples at once, and allows samples to be stored at room temperature for 5 days. Each test will cost only about US $18, compared to US $50 for the prevalent technique.