Washington ? Like a hummingbird following fragrance to a flower, the male sperm follows chemical attractants to find the female egg.

Researchers now have identified a key part of the process and say the discovery could lead to a new form of contraception that does not depend on hormones, or to help for infertility.

In laboratory tests, the researchers have found that human sperm has a receptor, or chemical sensor, that causes the sperm to swim vigorously toward concentrations of a natural attractant.

The precise compound present in the human female reproductive tract has not been identified, the researchers said. But the new study, using a laboratory compound called bourgeonal, proves that sperm does respond to a chemical signal by swimming toward the source, said Richard K. Zimmer, a professor of biology at UCLA and a co-author of the study appearing today in the journal Science.

Zimmer said the researchers also identified another compound, called undecanal, that shuts down the sperm receptor and keeps it from responding to an attractant.

Although much more research must be done, Zimmer said the twin discoveries could lead to new drugs that could, depending on their use, overcome some fertility problems or inhibit conception.

Some human reproduction researchers said the study by Zimmer and his co-authors was a significant advance in understanding how the sperm and egg find each other.

“This is a landmark piece of work,” said Dr. Donner F. Babcock, a researcher at the University of Washington in Seattle. “The holy grail in reproductive biology has been to find the sperm attractant and to understand how it works.

“This is the strongest evidence we have so far that the egg signals its location to the sperm and the sperm responds by swimming toward the egg,” Babcock said.

In the study, Zimmer and his co-authors at UCLA and the Ruhr University Bochum in Germany demonstrate that the surface of human sperm has a receptor that causes the sperm to navigate in a specific direction when it detects bourgeonal.