Many surveys have been conducted in different countries on the incidence of Cysticercus bovis and Echinococcus granulosus cysts in bovine carcasses. Abattoir findings of these two infections were given in the Annual Reports of the Department of Veterinary Services, Kenya (1954-58); the figures ranged between 20 and 35 percent for C. bovis; higher figures were for stock from African areas. The incidence of E. granulosus was 17 to 47 percent. Articles from other countries usually refer to only one condition. A comprehensive survey of the literature on occurrence and other aspects of cysticercosis was made by Viljoen (1937), who gave infection rates from most countries in the world. Since then, figures published include those of Jepson and Roth (1952) who reported less than 1 percent in Denmark in 1948, Silverman (1955) who found varying rates of 0.81 to 3.47 percent at different abattoirs in the United Kingdom, Simitch and Nevenitch (1955) who recorded 10 to 20 percent infection with C. bovis in different parts of Yugoslavia, and Peel (1953) who found 38.4 percent of 1,000 N'dama cattle infected at abattoir inspection in Sierra Leone. Pullar and Marshall (1958) who surveyed a large number of cattle in Australia for hydatid disease, recorded an overall 12 percent infection. Cyprus had the highest recorded incidence with up to 100 percent affected (Cyprus Dept. of Agr., 1957), while up to 90 percent of Yugoslavian stock was infected in some parts of the country (Nevenic, 1953). The infection rate in different districts of Chile varied from 0.6 to 86.3 percent (Neghme et al, 1951), and in Italy there was a variation from 1.5 to 42 percent according to Altara (1953). Pipkin and his co-workers (1951) reviewed the incidence in man and animals in the Near East and quoted several previous papers which showed that there was a cattle infection rate of 8.4 to 47 percent in that area. On the other hand, the United States of America appeared remarkably free, since an annual average of only 2,837 livers were condemned for hydatidosis in the period 1950 to 1957 from an average kill of 20 to 26 million cattle (Poole, 1957). The total infection rate was probably higher, as Schwartz (1957) pointed out in a discussion of Poole's paper, the liver: lung ratio being at least 2: 3, but this still gives a very low percentage compared with other countries. The present study in Kenya on 1,000 head of cattle was made chiefly to discover whether cysts of C. bovis and E. granulosus could occur in the same beast, or whether some interference occurred due to their relatively close generic relationship. Taliaferro (1930) quoted Meyer and others who stated that complement fixation cross reactions could be obtained with sera from persons infected with T. saginata and hydatid cysts against the heterologous antigens. Other workers did not confirm this. Miller (1932) reported that T. pisiformis material given intraperitoneally to rats conferred a high degree of protection against T. taeniformis. Coudert and Coly (1956) found that the serum of Taenia carriers agglutinated