Certain characteristics of 328 Mozambican male Shangaans with primary hepatocellular cancer (PHC) have been compared with those of 163 Shangaan men with hepatomegaly from causes other than PHC and with those of 122 Black Southern African men with the same tumour but who belonged to tribes other than the Shangaan. Shangaans with PHC were significantly younger than non-Shangaans with the tumour (mean age 33,4 cf. 40,0 years; Pless than 0,001). They also had a significantly higher positivity rate of alpha-fetoprotein by immunodiffusion (71,4%) than the non-Shangaans (16%), although in other respects the tumours appeared to be similar. Cirrhosis of the non-tumorous part of the liver was present at necropsy in 62% of the Shangaans and in 66% of the non-Shangaans. The hepatitis B (surface) antigen (HBsAg) was detected in the serum of 60% of the Shangaans with PHC compared with only 9% of the controls. The antigen was present in 53,4% of the non-Shangaans with PHC (the difference between this fifure and that in the Shangaans was not significant). HBsAg was detected in the serum of 64% of the Shangaans with PHC and cirrhosis, but also in 74% of those with the tumour without associated cirrhosis. The possible role of the hepatitis B verus in the aetiology of PHC is considered in the light both of these findings and of the possibility that the frequency with which the tumour is associated with cirrhosis may be decreasing in Shangaans. Some of the dietary habits of the Shangaans with PHC were compared with those of the controls. Virtually all the patients with PHC, but also almost all the controls, ate groundnuts in large quantities from an early age, as well as cashew nuts in smaller amounts. Cycad pips, mopani leaves and pods, mopani worms and locusts were not eaten by significantly more of the Shangaans with PHC than the controls. The limitations of this type of dietary analysis are discussed.