Sir

J. L. Heilbron and W. F. Bynum say, in their Commentary article about anniversaries of note that occur this year, that Stanley H. Cohen (Nobel prizewinner, 1986) and Herbert W. Bayer (sic) opened up the field of genetic engineering (Nature 391, 13–16; 1998).

The Stanley (no-initial) Cohen who received the Nobel prize for the discovery of epidermal growth factor is not the same as Stanley N. Cohen who laid the foundations of recombinant DNA technology along with Herbert Boyer (not Bayer), both of whom, in my view, also merit the prize.

Sir — J. L. Heilbron and W. F. Bynum mention that the US National Aeronautics and Space Administration (NASA) made history by putting into orbit three space stations called sky labs. In fact, Skylab was a single space station, launched unmanned, all up on 14 May 1973, and was visited by three successive three-man crews, the last of which departed on 8 February 1974.

On 11 July 1979, Skylab struck the Earth's surface, scattering debris from the southeastern Indian Ocean to Western Australia. Readers interested in Skylab can visit the NASA Web site (http://www.ksc.nasa.gov/history/skylab/skylab.html).