Within eight months of their taking up the appointments in St Petersburg Daniel's brother died of fever. Daniel was left, greatly saddened at the loss of his brother and also very unhappy with the harsh climate. He thought of returning to Basel and wrote to his father telling him how unhappy he was in St Petersburg. Johann Bernoulli was able to arrange for one of his best pupils, Leonard Euler, to go to St Petersburg to work with Daniel. Euler arrived in 1727 and this period in St Petersburg, which Daniel left in 1733, was to be his most productive time.
Sa loob ng walong buwan ng kanilang dinadala ang mga tipanan sa St Petersburg Daniel's kapatid na lalaki ay namatay ng lagnat. Daniel ay kaliwa, malaki saddened at ang pagkawala ng kanyang mga kapatid na lalaki at din masyadong nalulungkot sa malupit klima. He-iisip ng pagbabalik sa Basel at wrote sa kanyang ama sa kanya na nagsasabi kung paano malungkot siya sa St Petersburg. Johann Bernoulli ay makapag-ayos para sa isa sa kanyang pinakamahusay na mga nag-aaral, Leonard Euler, upang pumunta sa St Petersburg sa trabaho sa Daniel. Euler arrived in 1727 at panahong ito sa St Petersburg, na Daniel kaliwa sa 1733, ay kanyang pinaka-produktibong oras.