Subdivisions within a complete receptor code
| Structural class | 1.1–4.4 |
| Indicated by first two numbers; see tables 2-6 for description of associated codes. | |
| Receptor family | Alphanumeric code (up to six upper case characters, but |
| An endogenous agonist (or family of agonists) provides the receptor family code; see table 7 for recommended codes. | usually three) to be used (e.g., 5HT for 5-hydroxytryptamine or serotonin) |
| Receptor type | Alphanumeric code (up to five upper case characters) |
| See table 8 for examples. | consistent with the approved trivial name or number and its associated recognition and transduction characteristics |
| Species | Three upper case letters will code for species as used by |
| See table 9. | the Human Genome Database project |
| Splice or other sequence variant | 00–99 |
| Pair of numbers after species code; see table 10. | |
| Extra category | 00–99 |
| Pair of numbers after splice variant code. This is reserved for further subclassification purposes if considered desirable in the future. Where this and the preceding subdivision are not assigned, the zeros can be omitted for most purposes. | |
| Final letter code | .P, provisional RC (see text) |
| Single upper case letter preceded by a dot. | .S, receptor subunit |
| .M, multimeric receptor of known composition |