Mound-building termites were studied from 1976–1982 at Emali, Selengei and Ruaraka, three sites in semi-arid southern Kenya. The mounds, most of which were built by species of Macrotermes but some by Odontotermes species, contained 2–20 m³ of soil ha⁻¹. Mound dispersion was regular to a significant degree (implying intra-specific competition) at Emali and Selengei, but not at Ruaraka, where instead there was a distinct vertical zonation of species up a valley slope. Mound-building termites show evidence of intra-specific competition in other ways—for example, large mounds are further apart. Inter-specific competition was also apparent at Emali and there is evidence of inter-generic competition at Ruaraka but of inter-generic associations at Selengei. Building activity increased during wetter periods, whilst feeding, as reflected by the extent of earth coverings, was negatively correlated with rainfall, especially for the Macrotermes species. Ventilation shafts are numerous on large, unshaded mounds of M. subhyalinus, confirming the main purpose of the shafts, which may however limit the maximum size of mounds. M. michaelseni, which has no external openings, uses a different system for ventilation. Flighting by Macrotermes alates shows interesting variations between and within species whose full explanation will require further research.