Antimutagenic fractions from collards yielded indole-3-carboxaldehyde  and traces of indole-3-acetonitrile . The compounds had no antimutagenic activity. An analytical procedure for various indoles in plants was developed based on reversed-phase hplc. The indoles studied included the 3-carbinol 1, the acetonitrile 2, the carboxaldehyde 4, the 3-carboxylic acid 5, and the 3-acetic acid 6. Many Cruciferae and non-Cruciferae were analyzed. The latter did not contain measurable quantities of these compounds. In the case of the Cruciferae--with the exception of collards, which consistently indicated the presence of the aldehyde 4--major indole found was the nitrile 2. Although a particularly careful search for the carbinol 1 was conducted, only trace levels were noted. A review of the literature indicates that the content and occurrence of this indole in plants have been heavily overestimated. Because of the low levels found in the Cruciferae, our studies indicate that the role of the compound as a dietary factor may be questionable.