Commentary. In the article “Genetic code origins: Experiments confirm phylogenetic predictions and may explain a puzzle” by Paul Schimmel and Lluis Ribas de Pouplana, which appeared in number 2, January 19, 1999 of Proc. Natl. Acad. Sci. USA (96, 327–328), the following corrections should be noted. The fifth and sixth sentences of the first paragraph on page 328 should read as follows (changes are indicated by bold type): “This base pair is found in the spirochetes T. pallidum and B. burgdorferi that contain a class I enzyme. In contrast, Ibba et al. (1) show that the class II E. coli enzyme cannot accept G2-U71.” Also, the word “spirocytes” in the sixth sentence of the second paragraph on page 328 should read spirochetes. Finally, the sixth sentence of the last paragraph on page 328 should read as follows: “So multiple lateral gene transfer from archaebacteria to certain bacteria could account for the presence of class I LysRS in bacterial organisms such as T. pallidum, B. burgdorferi, and R. prowacekii.”