A new method of censusing breeding Swifts is described. It is based on ticking off holes under tiles and in walls which are entered by Swifts. Each entrance was scored and numbered during two complete surveys between 19 May and 25 June 1989. In the churches of Roden and Peize, respectively 130 and 52 pairs were thus localised. This is substantially more than the 24 and 10-20 pairs which were counted by a different method in 1987, viz. by visiting the colonies in the evening and dividing the number of birds present by two. The former estimate of the number of breeding Swifts in the province of Drenthe (1150-1380 in 1981-87) was probably too conservative; a new estimate of 4000 pairs is suggested.