With a synthetic oligonucleotide mixture as probe, complementary DNA clones of C-reactive protein were isolated from an adult human liver complementary DNA library. The clones ranged in size from 700 to 1100 base pairs and were identified by partial DNA sequence analysis. One complementary DNA clone was used as a probe for hybridization with human-rodent DNA's isolated from somatic cell hybrids and bound to nitrocellulose filters (Southern blot analysis) to assign the human C-reactive protein gene to chromosome 1.