The Encyclopedia of Beekeeping (Morse & Hooper 1885) suggest a sample of 30 bees for disease diagnosis (in those days it was only acarine, nosema and amoeba that we had to worry about - apart from the foulbroods), giving the reason for the sample size as the following table of probabilities: Percentage of infected Number of bees to be examined to give the indicated bees in colony percentage chance of finding at least one diseased bee 80% 90% 99% 90 1 2 2 80 1 2 3 70 2 3 4 60 2 4 5 50 3 5 7 40 3 6 9 30 5 8 13 20 7 13 21 15 10 18 28 10 15 28 44 5 31 58 89 1 161 298 457 (Hope this table formats OK!) So by taking a sample of 30 bees, we have (approximately) a 95% chance of finding a diseased bee if 10% of the colony is diseased or an 80% chance if only 5% is diseased. Using the table, you can decide on the sample size necessary to give you the level of confidence that you require. Peter Edwards