Fertile Macrocystis pyrifera (L.) C. Ag. and Pterygophora californica Rupr. were collected in California, USA in 1987 to 1988. Spores of the kelps exhibited both positive and negative chemotaxis to a variety of chemical nutrients. Chemotaxis was measured by counting the number of spores that swam into flattened capillary tubes with the chemical relative to the number that swam into control tubes. Video-motion-analysis also showed that P. californica spores swam towards a nitrogen source more often than they swam away. Similar chemotactic effects were observed in both 2 and 8 h-old preparations. M. pyrifera spores swam towards nitrate, ammonium (1 to 90 μM), glycine, aspartate iron (1 μm), boron, cobalt, and manganese. Negative chemotaxis was elicited by ammonium (1 000 μM) and iron (45 μM). Neither phosphate nor zinc had significant effects. P. californica spores were attracted by nitrate, ammonium, phosphate, and boron. Negative chemotactic effects were recorded with iron (45 μM) and manganese. Iron (1 μM), cobalt, and zinc had no effect. It is suggested that chemotactic behavior is an adaptation which allows the kelp spores to find and settle in microhabitats suitable for gamatophytic growth and reproduction. © 1989 Springer-Verlag.