This study is investigating the safety and tolerability of the new medicine NNC0268-0965 (referred to as insulin 965), its concentrations in the blood and its effect on blood sugar for the treatment of diabetes. This first part of the study is conducted in healthy people, while there is a second part involving people with type 1 diabetes. The study will test how insulin 965 is tolerated by the participants' body, how it is taken up in the participants' blood, how long it stays there and how blood sugar is lowered. Participants will either get the new insulin 965 or placebo (an injection that does not contain active medicine) - which treatment you get is decided by chance. It is the first time that insulin 965 is tested in humans. Participants will get one injection of either insulin 965 or placebo under the skin of the left thigh. The study will last for about 5 weeks. Participants will have 6 clinic visits with the study doctor. People cannot be in the study if the study doctor thinks that there are risks for their health.

Inclusion Criteria:

• Part 1 (healthy subjects):

  1. Male, aged 18-55 years (both inclusive) at the time of signing informed consent.

• Part 2 (subjects with type 1 diabetes mellitus):

  1. Male or female, aged 18-55 years (both inclusive) at the time of signing informed consent.
  2. Diagnosed with type 1 diabetes mellitus equal to or more than1 year prior to the day of screening.
  3. Male subject or female subject of non-child bearing potential. Non-child bearing potential being surgically sterilized (i.e. documented hysterectomy, bilateral salpingectomy or bilateral oophorectomy or being postmenopausal (as defined as no menses for 12 months without an alternative medical cause).
  4. Current daily total insulin treatment between 0.2 (I)U/kg/day and 1.2 (I)U/kg/day (both inclusive).
  5. HbA1c equal to or below 8.5%.
  6. Fasting C-peptide below 0.30 nmol/L.

Exclusion Criteria:

• (Part 1 and Part 2) 1. Male of reproductive age who or whose partner(s) is not using adequate contraceptive methods (adequate contraceptive measures as required by local regulation or practice). Adequate contraceptive measures include that the male subject uses a condom during intercourse and that the partner practices adequate contraception (risk of pregnancy must be lower than 1%). In addition, subjects must not donate sperm for the duration of the trial.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com

Sponsor staff involved in the clinical trial is masked according to company standard procedures.