It is acknowledged that contrast plays an important role in understanding discourse and information structure. While it is commonly assumed that contrast can be marked by intonation only, our understanding of the intonational realization of contrast is limited. For German there is mainly introspective evidence that the rising theme accent (or topic accent) is realized differently when signaling contrast than when not. In this article, the acoustic basis for the reported impressionistic differences is investigated in terms of the scaling (height) and alignment (positioning) of tonal targets. Subjects read target sentences in a contrastive and a noncontrastive context (Experiment 1). Prosodic annotation revealed that thematic accents were not realized with different accent types in the two contexts but acoustic comparison showed that themes in contrastive context exhibited a higher and later peak. The alignment and scaling of accents can hence be controlled in a linguistically meaningful way, which has implications for intonational phonology. In Experiment 2, nonlinguists' perception of a subset of the production data was assessed. They had to choose whether, in a contrastive context, the presumed contrastive or noncontrastive realization of a sentence was more appropriate. For some sentence pairs only, subjects had a clear preference. For Experiment 3, a group of linguists annotated the thematic accents of the contrastive and noncontrastive versions of the same data as used in Experiment 2. There was considerable disagreement in labels, but different accent types were consistently used when the two versions differed strongly in F0 excursion. Although themes in contrastive contexts were clearly produced differently than themes in noncontrastive contexts, this difference is not easily perceived or annotated. (Contains 10 tables, 9 figures, and 11 footnotes.)