Sinusoidal fetal heart rate (SHR) records were obtained in 8 cases, either antepartum (3 cases of fetal Rh disease) or intrapartum (one case with an acute episode of fetomaternal transfusion as possible cause, 2 after meperidine administration to the mother and 2 others without attributable causes). Characteristics of both SHR patterns and related clinical pictures are described and compared to similar cases published elsewhere. The possible underlying mechanisms of SHR are discussed. Two different profiles of SHR patterns (smooth and jagged waveforms) are characterized and correlated with their most usual clinical backgrounds and prognostic significance. A classification of SHR into 2 main types is proposed, with clinical use in mind.