In acoustic theory, formant pattern differences within one vowel identify are related to differences in the speaker groups or in the types of vocalization. Yet, studies of vowel synthesis indicate that formant patterns can also vary strongly in relation either to pitch or to formant number alterations. Within this study, natural vocalizations of nine German vowels were investigated with regard to different formant patterns representing the same vowel identity, apart from differences in speaker groups and vocalization types. The results show i) FO-dependence of the lower formants < 1.5-2 kHz; ii) occurrence of natural one-formant back and two-formant front vowels; iii) a non-systematic relationship between FO and the formants, and a non-systematic relationship between formant patterns of different formant numbers. The implications for psychophysics, physiology and perception of speech are discussed.