An investigation of lung tissue samples from sudden unexpected infant deaths from the German Democratic Republic (G.D.R.) (n = 106) and Finland (n = 94) shows the German material to contain 54 cases (51%) with advanced inflammatory changes allowing a definite pathologico-anatomical diagnosis and explanation for the death, whereas there were only 19 such cases (20%) in the Finnish material. Slight changes indicating an inflammatory process but not allowing a definite diagnosis ("borderline cases") were seen in one fifth of the cases in both countries. Thus a greater proportion of the child deaths below the age of 1 year in Finland are real cot deaths than in the G.D.R. where signs of respiratory infection can be found more often.