We introduce two new nondigestible solid markers for gastrointestinal transit measurements. One is technetium-99m-labeled cellulose fiber [99mTc]CF, the other is indium-111-labeled plastic particles [111In]PP of 2- to 3-mm diameter. In six healthy male volunteers gastric emptying and small intestinal transit of the two markers were obtained simultaneously. Large intestinal transit of [111In]PP was also obtained. Technetium-99m CF had acceptable stability properties in the proximal gastrointestinal segments. Indium-111 PP was almost completely stable in all segments. Mean gastric emptying time was 1.13 +/- 0.24 hr (mean +/- s.d.) for [99mTc]CF and 1.94 +/- 0.78 hr for [111In]PP. The difference was significant (p less than 0.05). Mean small intestinal transit time was 3.85 +/- 0.61 hr (mean +/- s.d.) for [99mTc]CF and 4.03 +/- 0.34 hr for [111In]PP. The difference was not significant (p less than 0.5). Mean large intestinal transit time of [111In]PP was 23 +/- 11 hr (mean +/- s.d.). We also suggest a simple deconvolution principle for the interpretation of the small intestinal and the large intestinal transit data.