Rotational line strengths (Hönl–London factors) are calculated for 3Σ±–3Σ± electric dipole transitions, allowing for nonzero values of the splitting constant λ. If the 3Σ states are intermediate between Hund's coupling cases (a) and (b) only one transition moment is required, whereas if there is a tendency to case (c) four transition moments may be required. The resulting formulas are compared with the observed spectra of the diatomic molecules of the Group VI elements. The same formulas are valid for 3Σ±–3Σ± magnetic dipole transitions.